Forensic psychology

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Forensic_psychology 

Forensic psychology involves the generation of both basic and applied psychological science relevant to the law, as well as application of psychological knowledge and methods to help answer legal questions arising in civil, criminal, contractual, or administrative proceedings. Historically, forensic psychology was defined narrowly as the application of clinical psychological knowledge to criminal cases or questions in criminal justice settings. Contemporary definitions of forensic psychology recognize that several subfields of psychology apply "the scientific, technical, or specialized knowledge of psychology to the law." While the American Psychological Association (APA) officially recognized forensic psychology as a specialty under the narrower definition in 2001, the Specialty Guidelines for Forensic Psychologists were revised in 2013 and now reference several psychology subdisciplines, such as social, clinical, experimental, counseling, and neuropsychology).

History

See also: History of psychology

 

Front cover of an early edition of Hugo Muensterberg's "On the Witness Stand" book

Psychology was established in the U.S. in 1879 by American students returning home from studying in German psychologist Wilhelm Wundt's experimental psychology lab. Many of these returning students had interests in law (e.g. testimonies, individual's functional capacity) in addition to the schools of the field taught by Wundt. Nonetheless, the concept of psychology being officially used in legal settings wasn't introduced until several years later, in the first decade of the 20th century by Hugo Münsterberg, the first director of Harvard's psychological laboratory and founder of applied psychology. Though he attempted to imbue his expertise in the legal field, such as through his On the Witness Stand book, his approach was reported as being condescending and abrasive, causing anger and scrutinization from the legal community toward his research, such as by the influential legal scholar John Henry Wigmore.

Following this backlash, psychology was widely left untouched by legal professionals until post-WWII, when clinical psychology became more accepted as a legitimate health profession and became more successful in contributing to legal proceedings. Whereas cases such as Brown v. Board of Education of Topeka (1954) led to the appreciation of psychology's ability to influence legal decisions, it was cases like Jenkins v. United States (1962) that truly legitimized it. In this latter case, Justice David Bazelon of the D.C. Circuit Court of Appeals upheld, for the first time - and relatively uniquely internationally - that psychologists could testify as medical experts about mental illness.

The American Psychology-Law Society (AP-LS) was created in 1969 and was later converted into Division 41 of the APA in 1980. As the field continued to grow, more organizations dedicated to the study and application of psychology to the law began to develop. In 1976 the American Board of Forensic Psychology (ABFP) was chartered and eventually became a part of the American Board of Professional Psychology (ABPP) in 1985. This merging marked the development of the first certification for psychologists wanting to work within the field of forensic psychology. Later organizations and conferences aided in solidifying the development of forensic psychology, such as the American Academy of Forensic Psychology and the National Invitational Conference on Education and Training in Forensic Psychology (1995). Forensic psychology was then officially recognized as a professional specialty under the APA in 2001.

Forensic psychology in popular culture

Within recent years, forensic psychology has seen a large spike in popularity in the media and among younger generations. For example, many recent docuseries on Netflix feature forensic psychological content, including Making a Murderer and Sins of our Mother. Many undergraduate students are drawn to this subject under the misconception that forensic psychology is primarily used for criminal profiling. TV shows and movies such as Criminal Minds, Manhunter, Mindhunter, and Silence of The Lambs have widely popularized the practice of criminal profiling, particularly within the Federal Bureau of Investigation's (FBI) Behavioral Analysis Unit (BAU). Despite the excitement given to the idea of a career in criminal profiling, students who show an interest in this particular aspect of forensic psychology come to find that the practice of criminal profiling is rarely used outside of the BAU. They also find that there are many forensic psychology practices outside criminal proceedings.

Training and education

In a broad sense, forensic psychology is a subset of applied psychology. Forensic psychologists may hold a Ph.D. or Psy.D. in clinical psychology, counseling psychology, social psychology, organizational psychology, school psychology, or experimental psychology. There are no specific license requirements in the United States to be a forensic psychologist. If one is a clinical-forensic psychologist, one would need a license to practice clinical or "health services", but an additional license to practice clinical-forensic psychology is not required. Psychologists who do not provide healthcare services do not need to be licensed at all in some states. Forensic psychologists ideally have some years of postdoctoral experience, training, and supervision or mentoring in forensic psychology.

In other countries, training and practitioner requirements may vary. In the United Kingdom, for example, a person must obtain the Graduate Basis for Registration with the British Psychological Society – normally through an undergraduate degree. This would be followed by Stages 1 (academic) and 2 (supervised practice) of the Diploma in Forensic Psychology (which would normally take 3 years full-time and 4 years part-time). Assessment occurs via examination, research, supervised practice, and the submission of a portfolio showing expertise across a range of criminological and legal applications of psychology. Once qualified as a "chartered" psychologist (with a specialism in forensic psychology), a practitioner must engage in continued professional development and demonstrate how much and of what kind, each year, in order to renew their practicing certificate.

Roles of a forensic psychologist

Practice/direct service

Evaluations and assessments

Evaluations and assessments are completed by forensic psychologists to assess a person's psychological state for legal purposes. Reasons for completing these evaluations can involve acquiring information for criminal court (such as insanity or incompetence), for criminal sentencing or parole hearings (often regarding a potential intellectual disability that prevents sentencing or one's risk of recidivism), for family court (including child custody or parental termination cases), or civil court (involving, for example, personal injury or competence to manage one's financial affairs). It is important to note that while a forensic psychologist is responsible for assessing and reporting results of an evaluation, they do not make decisions on "ultimate issues" such as competence to stand trial or service-connected disability for U.S. military veterans.

Forensic psychological evaluations do not constitute treatment or the provision of healthcare services.

Treatment

Treatment providers may be asked to administer psychological interventions to those who require or request services in both criminal and civil cases. In regard to criminal cases, forensic psychologists can work with individuals who have already been sentenced to reduce recidivism, which refers to one's likelihood of repeating his or her offense. Other interventions that may be implemented in these settings are substance use disorder treatment, sex offender treatment, treatment for a mental illness, or anger management courses. As for civil proceedings, treatment providers may have to treat families going through divorce or custody cases. They may also provide treatment to individuals who have suffered psychological injuries as a result of some kind of trauma. Treatment providers and evaluators work in the same types of settings: forensic and state psychiatric hospitals, mental health centers, and private practices.

Consultations

Providing consultations allows forensic psychologists to apply psychological expertise and research to help law enforcement, attorneys, and other legal professionals or proceedings better understand human behavior (e.g. criminal, witness, victim, jury), civil processes, effects of trauma or other life events, and so on. If working as a consultant, a forensic psychologist is able to be involved in legal proceedings through responsibilities such as reviewing court records (such as a defendant's psychosocial history or assess mitigating or aggravating factors in a case), serving as a jury consultant (organizing focus groups, shadow juries, mock juries, or helping with the voir dire proceedings), and assessment without testimony (in which results of a defendant's evaluation are not disclosed to the prosecution team, allowing the defense team to develop a defense strategy), among others. Essentially, consultations can take a number of forms, including the common ones below:

Law enforcement consultations may take the form of assisting with criminal profiling, developing hiring procedures and methods, determining the psychological fitness of returning officers, or simply lending expertise on certain criminal behaviors. There are several methods and approaches related to criminal profiling, but there is a lot of skepticism and criticism about the efficiency and accuracy of criminal profiling in general. A couple common approaches are the scientific approach, which includes the FBI's Crime Scene Analysis and Canter's Investigative Psychology, and the intuitive approach, which includes Tukey's Behavioral Evidence Analysis.

Trial consultants are psychologists who work with legal professionals, such as attorneys, to aid in case preparation. This includes jury selection, development of case strategy, and witness preparation. Forensic psychologists working as trial consultants rely on research in order to best advise the individuals they are working with. Because trial consultants are often hired by one specific side in a trial, these psychologists are faced with many ethical issues. It is the responsibility of the psychologist to remain neutral when consulting – in other words, the consultant must not choose a side to support and consequentially omit or create information that would be beneficial to one side or another. Prior to accepting a case to work on, it is important that the forensic psychologist weigh the responsibilities of consulting on that case with the ethical guidelines put in place for the field of forensic psychology.

Expert testimony about matters relating to psychology is also an area in which forensic psychologists play an active role. Unlike fact witnesses, who are limited to testifying about what they know or have observed, expert witnesses have the ability to express further knowledge of a situation or topic because, as their name suggests, they are presumed to be "experts" in a certain topic and possess specialized knowledge about it. Procedural and legal rules guide expert testimony, which include that the evidence must be relevant to the case, the method the expert used must be valid and reliable, and that the evidence will help the trier of fact. An expert can be deposed by opposing counsel to discover what they plan to say in court, and attorneys have the opportunity to raise a challenge to the admissibility of the expert's testimony if there are questions about its relevance, or its validity and reliability (in the United States - the rules vary by country and jurisdiction). Regardless of who calls in the expert, it is the judge who determines whether or not the expert witness will be accepted through a voir dire process of qualification.

Research

Forensic psychology researchers make scientific discoveries relevant to psychology and the law and they also sometimes provide expert witness testimony. These professionals usually have an advanced degree in psychology (most likely a PhD). These professionals may be employed in various settings, which include colleges and universities, research institutes, government or private agencies, and mental health agencies. Researchers test hypotheses empirically regarding issues related to psychology and the law, such as jury research and research on mental health law and policy evaluation. Their research may be published in forensic psychology journals such as Law and Human Behavior or Psychology, Public Policy, and Law, as well as more broadly in basic psychology journals. Some famous psychologists in the field include Scott Lilienfeld who was widely known for his scholarship on psychopathology and psychopathy, Saul Kassin who is widely known for studying false confessions, Jennifer Skeem who is widely known for studying justice-involved people with mental illness, Michael Saks who is known for his contributions to jury research and improvements to forensic science, Barbara Spellman who is known for her cognitive psychology-law work as well as for her open science leadership, and Elizabeth Loftus and Gary Wells who are both known for their research on eyewitness memory.

Education and advocacy

Academic forensic psychologists engage in teaching, researching, training, and supervision of students, among other education-related activities. These professionals also have an advanced degree in psychology (most likely a PhD) and are most often employed at colleges and universities. In addition to holding professorships, forensic psychologists may engage in education through presenting research, hosting talks relating to a particular subject, or engaging with and educating the community about a relevant forensic psychology topic. Advocacy is another form of education, in which forensic psychologists use psychological research to influence laws and policies. These may be related to certain movements, such as Black Lives Matter or the Me Too movement, or may even be related to certain civil rights that are being overlooked.

Forensic psychological evaluations

Common types of evaluations

Forensic assessment of competence

Competence, in a legal setting, refers to the defendant's ability to appreciate and understand the charges against them and what is happening in the legal proceedings, as well as their ability to help the lawyer understand and defend their case. While competence is assessed by a psychologist, its concern regarding a defendant is typically voiced by the lawyer. Though it is the psychologist's responsibility to assess for competence, it is ultimately up to the judge to decide whether the defendant is competent or not. If the defendant is found incompetent to stand trial, the psychologist must then give a recommendation on whether or not the defendant can be restored to competence through treatment or if the charges should be dropped completely due to incompetence. A couple potential causes of incompetence include certain types of brain damage or the occurrence of a psychotic episode preventing the individual from registering the reality around them.

Several cases were instrumental in developing a standard for competence, as well as for determining the rights of an individual deemed incompetent to stand trial. Youtsey v. United States (1899) was one of the cases that set the standard for competence, with the judge ruling that trying or sentencing an individual deemed incompetent violates their human rights. Despite this ruling, no official guidelines for determining and sentencing matters of competence were developed. In Dusky v. United States (1960), the case upheld the Youtsey v. United States ruling and set specific criteria for competence. These include having a rational and factual understanding of court proceedings and being able to consult with an attorney in a rational manner. The case of Weiter v. Settle (1961) resulted in the decision that a psychologist's opinion in a competency hearing is considered "opinion testimony." Additionally, guidelines were put in place to accurately evaluate competency. The eight guidelines established include requirements that the defendant appreciates one's own presence in relation to time, place, and things; understands that they are in a Court of Justice, charged with a criminal offense; recognizes that there is a Judge who presides over the Court; understands that there is a Prosecutor who will try to convict them of criminal charges; understands that they have a lawyer who will defend them against that charge; knows that they are expected to tell their attorney what they were doing at the time of the alleged offense; understands that a jury will determine whether they are guilty or innocent of the charges; and has sufficient memory to discuss issues related to the alleged offense and the court proceedings. As time has progressed, more cases have added to these guidelines and expectations when evaluating competency.

Forensic assessment of insanity

Insanity, as opposed to competence, refers to an individual's mental state at the time of the crime rather than at the time of the trial. According to legal principles of insanity, it is only acceptable to judge, find someone criminally responsible, and punish a defendant if that individual was sane at the time of the crime. In order to be considered sane, the defendant must have exhibited both mens rea and actus reus. Mens rea, translated to "guilty mind", indicates that the individual exhibited free will and some intent to do harm at the time of the crime. Actus reus refers to the voluntary committing of an unlawful act. The insanity defense acknowledges that, while an unlawful act did occur, the individual displayed a lack of mens rea. The burden of proof in determining if a defendant is insane lies with the defense team. A notable case relating to this type of assessment is that of Ford v. Wainwright, in which it was decided that forensic psychologists must be appointed to assess the competency of an inmate to be executed in death penalty cases.

There are various definitions of insanity acknowledged within the legal system. The M'Naghten/McNaugton rule (1843) defines insanity as the individual not understanding the nature and quality of his or her acts or that these acts were wrong due to a mental disease or defect. This is also referred to as the cognitive capacity test. Meanwhile, the Durham Test (established in Durham v. United States, 1954) states that one can be declared insane if the actions were caused by a mental disorder. The vague nature of this description causes this definition to only be used in one state (New Hampshire). The final definition acknowledged within the courts is the Brawner Rule (U.S. v. Brawner, 1972), also referred to as the American Law Institute Standard. This definition posits that, due to a mental disease or defect, an individual is considered insane if unable to appreciate the wrongfulness of an act and are unable to conform their behavior to the dictates of the law.

Evaluating insanity involves using crime scene analysis to determine the mental state at the time of the crime, establishing a diagnosis, interviewing the defendant and any other relevant witnesses, and verifying impressions of the defendant. Challenges associated with this type of assessment involve defendant malingering, determining the defendant's past mental state, the chance that different experts may come to different conclusions depending on the assessment method used, and the fact that it is very common for society to label any psychological disorder as insane (though few actually fall into this category; insanity primarily involves psychotic disorders).

Risk assessment

Risk assessment evaluates how dangerous an individual is or could be and the risk of them re-offending after being released, also referred to as recidivism. Typically, recidivism refers to violent or sex offending behavior. Risk assessments affect the possibility of an inmate receiving parole or being released from prison and involve two general methods. The clinical prediction method involves using clinical judgement and experience to predict risk, while the actuarial prediction method utilizes a research-based formula to predict risk. Two specific methods of risk assessment involve the Violence Risk Appraisal Guide (VRAG) and the Sex Offender Risk Appraisal Guide (SORGA), both created by Quinsey, Harris, Rice, & Cormier in 1998.

Other types of evaluations

While insanity and competency assessments are among the most common criminal assessments administered within the legal system, there are several other types implemented. Some of these include death penalty case assessments, assessments of child sexual abuse, assessments for child custody or divorce cases, and civil court assessments.

Distinction between forensic and therapeutic evaluation

A forensic psychologist's interactions with and ethical responsibilities to the client differ widely from those of a psychologist dealing with a client in a clinical setting.

• Scope. Rather than the broad set of issues a psychologist addresses in a clinical setting, a forensic psychologist addresses a narrowly defined set of events or interactions of a nonclinical nature.
• Importance of client's perspective. A clinician places primary importance on understanding the client's unique point of view, while a forensic psychologist is interested in accuracy, and the client's viewpoint is secondary.
• Voluntariness. Usually, in a clinical setting, a psychologist is dealing with a voluntary client. A forensic psychologist evaluates clients by order of a judge or at the behest of an attorney.
• Autonomy. Voluntary clients have more latitude and autonomy regarding the assessment's objectives. Any assessment usually takes their concerns into account. The objectives of a forensic examination are confined by the applicable statutes or common law elements that pertain to the legal issue in question.
• Threats to validity. While the client and therapist are working toward a common goal, although unconscious distortion may occur, in the forensic context there is a substantially greater likelihood of intentional and conscious distortion.
• Relationship and dynamics. While therapeutic interactions work toward developing a trusting, empathic therapeutic alliance, a forensic psychologist may not ethically nurture the client or act in a "helping" role, as the forensic evaluator has divided loyalties and there are substantial limits on confidentiality they can guarantee the client. A forensic evaluator must always be aware of manipulation in the adversary context of a legal setting. These concerns mandate an emotional distance that is unlike a therapeutic interaction.
• Pace and setting. Unlike therapeutic interactions which may be guided by many factors, the forensic setting with its court schedules, limited resources, and other external factors places great time constraints on the evaluation without opportunities for reevaluation. The forensic examiner focuses on the importance of accuracy and the finality of legal dispositions.

Psychological autopsy

When the nature or cause of death remain unknown from the immediate and apparent features of death, especially due to the lack of direct evidence to determine whether the unnatural death is accidental, suicide, or murder, a psychological or psychiatric autopsy can be employed as an effective tool for death investigations.

The 'psychological autopsy' is a procedure for investigating a person's death by reconstructing what the person thought, felt, and did preceding their death. This reconstruction is based upon information gathered from personal documents, police reports, medical and coroner's records, and face to face interviews with family members, friends, and others who had contact with the person before the death.

While a medico-legal autopsy examines the body of the deceased, a psychological autopsy considers the mental state of the deceased. When there is conflict or absence of leads which indicate the circumstances pointing towards more than one possibility of mode of death (more specifically, the manner of death is suspicious and giving divergent indications), this tool of investigation can be employed with team work of forensic psychiatrists, forensic pathologists, toxicologists, and psychologists to compile information about the behaviors and motive to distinguish among accident, homicide, and suicide as possible modes of death.

The theory underlying the concept of psychological autopsy is that most suicide victims communicate their intentions in some way. While the technique was developed as a clinical tool for predicting suicide risk, its forensic application has been the retrospective determination of the cause or circumstances surrounding a death. This branch of investigation was originally developed by Edwin Shneidman and his colleagues in the Los Angeles Suicide Prevention Center during the 1950s.

Methodology

The psychological autopsy methodology involves two main elements: extensive interviews of family members and other close intimates, and collecting all possible medical, psychiatric, and other relevant documents of the deceased.

Psychological autopsies review the specifics of the death and the decedent for suicide risk factors. Shneidman for example, has identified 14 areas for inquiry in psychological autopsy studies. These areas include:

1. Identifying information (e.g., age, marital status, religious practices, occupation)
2. Details of the death
3. Brief outline of the victim's history (e.g., previous suicide attempts)
4. Death history of the victim's family (e.g., family history of suicide, affective illness)
5. Description of the personality and lifestyle of the victim
6. The victim's typical pattern of reaction to stress, emotional upsets, and periods of disequilibrium
7. Recent stressors, tensions, or anticipations of troubles
8. The role of alcohol and drugs in the overall lifestyle of the victim and their death
9. The nature of the victim's interpersonal relationship
10. Changes in the victim's habits and routines before death (e.g., hobbies, appetite, sexual patterns, and other life routines)
11. Information relating to the life side of the victim (e.g., upswings, successes, plans)
12. Assessment of intention
13. Rating of lethality
14. Reaction of informants to the victim's death, and
15. Any comments or special features of the case.

The information collected from the interviews could provide relevant information in an attempt to reconstruct the deceased's background, personal relationships, personality traits, and lifestyle. Psychological autopsies have proved helpful in identifying and explicating proximate causation, determining the role of a variety of factors in bringing about a suicide death.

The usual sources of psychological information are:

1. Suicide note – Interpretation of the suicide note is important to confirm suicide, abetment of suicide, or homicide, or to identify causation. The correct interpretation of a suicide note requires a handwriting expert to confirm that the note is written by the subject as its contents may reveal the following:
   1. Intention – It is reflected from the suicide note that the individual has killed themself. This intention is strengthened by a history of previous attempts.
   2. Physical illness – The changes in handwriting; for example, tremors (due to alcoholism, drug poisoning, fear, or anxiety) or changes in the size of letters (gradually becoming smaller due to intake of antipsychotic drug) may indicate presence of physical illness.
   3. Psychiatric illness – The contents of the suicide note may indicate the presence of a psychiatric disorder such as schizophrenia.
   4. Situational factors – Whether the individual is threatened or the suicide note is dictated.
   Example: good content by an illiterate individual, repeated cutting or suicide pact (suicide note signed by more than one individual or simple contents in different notes), or suicide intent of another person or abetment of suicide.
2. School/college records – Information such as a change in academic performance or recent absences and tardiness.
3. Medical records – Family history, visits to physician, illness, medication taken, and referrals to specialists.
4. Police records – May give information about previous attempts of suicide and involvement in anti-social activities.

The psychological autopsy is accomplished through reconstruction of the deceased's character and personality from information gained from a variety of sources. This reconstructed character and personality is then used to make a retrospective prediction of the likelihood of the deceased having committed a particular act. If the data collected and the analysis of the same conclude that there is no indication of suicide, the possibility of the deceased committing suicide can be ruled out.

Advantages and disadvantages

By collecting information from the people who are maintaining direct or indirect interactions, the personality of the deceased is most accurately described and assessed, which becomes the most significant input to evaluate the thought process and traits of the deceased prior to death. The evaluation involves the understanding of the intention and motive, if it is a suicide. If the autopsy negates the suicide, it will be useful for the investigators to proceed with the investigation of death by excluding the theory of suicide in the incident. The psychological autopsy provides a firm indication to which directions the death investigation should proceed.

Though the psychological autopsy can be an effective tool for suspicious death investigations, it is not free from disadvantages and limitations. The availability and selection of experts who have research oriented experience is always an important hurdle to get over. Professional ethics and physician-patient privileges are always a difficult barrier to getting valuable and important inputs. The end process of the psychological autopsy is the retrospective prediction of whether or not the subject has committed suicide. This process is being carried out by experts who had no occasion to meet or interview the deceased in their lifetime. The experts gather the information from third parties and documents, which could be considered as hearsay information which diminishes the evidentiary value. There is no standardised operational method to derive conclusions out of the information collected during the course of the psychological autopsy. It has to be drawn up by the professional and is largely based on their experience to correlate the inputs.

The psychological autopsy is one of the most effective tools in death investigations. It could act as a firm stepping stone for investigating a suspicious unnatural death where direct evidence is not available. Systematically carried out psychological autopsies could provide more scientific and accurate leads in death investigations.

In India, the employment of this branch of forensic psychiatry is less used. On 12/02/2016, the Chief Judicial Magistrate Court, Ernakulam, Kerala, has directed the Central Bureau of Investigation to employ a forensic psychological autopsy in the death investigation of Qazi C.M.Abdulla Maulavi of Chembarika. Thereafter in Sunanda Pushkar Death case, the Special Team for investigation has performed a psychiatric autopsy and concluded that it was a suicide. Another incident of employing this tool was in the Burari Death case in Delhi, in which 11 members of a family were found dead by hanging on 01/07/2018. The question in these cases to be answered was whether it is a suicide or homicide. The availability of experts in this area including experienced suicidologists is a concern of the time, as numerous reports are there regarding the increasing incidents of suicide. So there shall be sufficient concern for the state of establish research centres and institutions concentrated in this branch of forensic psychiatry.

Another aspect of concern is the extension of rigor to the hearsay rule in accepting the information and conclusions of psychological autopsies. The opinion evidence given by the experts who conducted the systematic psychological autopsy shall be given due weight taking the purview under Section 45 of the Evidence Act, 1872.

Ethics in forensic psychology

The ethical recommendations and expectations outlined for forensic psychology specifically are listed in the APA's Specialty Guidelines for Forensic Psychology. These guidelines involve reminders that forensic psychologists should value integrity, impartiality, and fairness, as well as avoid conflicts of interest when possible. These conflicts of interest may arise in situations in which the psychologist is working as a consultant to one side or another in a court case, when the psychologist is required to testify or evaluate something that collides with their own beliefs or values, or when a psychologist is faced with the decision of choosing between playing the role of an individual's evaluator or treatment provider in a case. This final conflict of interest also relates to the ethical guidelines relating to having multiple relationships with clients. As a standard of ethics, forensic psychologists are expected to offer a certain amount of reduced fee or pro bono services for individuals who may not be able to afford hiring a psychologist for a court case otherwise. Other ethical guidelines involve receiving informed consent from clients before communicating information regarding their treatment or evaluations, respecting and acknowledging privacy, confidentiality, and privilege among clients, remaining impartial and objective when involved in a trial, and weighing the moral and ethical costs of complying with any court orders that may conflict with professional standards.

Salary of a forensic psychologist

There is a wide range of pay for individuals in the forensic psychology field. In the United States, the median annual income is $125,000 - $149,999, and the pay can range from $50,000 (entry-level) a year to more than $350,000 a year. There are also pay differences for men and women, where women forensic psychologists earn $0.83 for every $1.00 men make. The pay for a forensic psychologist can also vary by the state that the forensic psychologist works in.

Notable research in forensic psychology

• Garry, Maryanne; Manning, Charles G.; Loftus, Elizabeth F.; Sherman, Steven J. (1996-06). "Imagination inflation: Imagining a childhood event inflates confidence that it occurred". Psychonomic Bulletin & Review. 3 (2): 208–214. doi:10.3758/BF03212420. ISSN 1069-9384.
• Harris, Paige B.; Boccaccini, Marcus T.; Murrie, Daniel C. (2015-08). "Rater differences in psychopathy measure scoring and predictive validity". Law and Human Behavior. 39 (4): 321–331. doi:10.1037/lhb0000115. ISSN 1573-661X.
• Holcomb, Matthew J.; Jacquin, Kristine M. (2007-07-03). "Juror Perceptions of Child Eyewitness Testimony in a Sexual Abuse Trial". Journal of Child Sexual Abuse. 16(2): 79–95. doi:10.1300/J070v16n02_05. ISSN 1053-8712.
• Kassin, S. & Wrightsman, L. (1980). Prior confessions and mock juror verdicts. Journal of Applied Social Psychology, 10, 133 146.
• Kassin, Saul M.; Drizin, Steven A.; Grisso, Thomas; Gudjonsson, Gisli H.; Leo, Richard A.; Redlich, Allison D. (2010). "Police-induced confessions: Risk factors and recommendations". Law and Human Behavior. 34 (1): 3–38. doi:10.1007/s10979-009-9188-6. ISSN 1573-661X.
• Loftus, Elizabeth F (1975-10). "Leading questions and the eyewitness report". Cognitive Psychology. 7 (4): 560–572. doi:10.1016/0010-0285(75)90023-7.
• Neal, T.M.S., Slobogin, C. Saks, M.J., Faigman, D., & Geisinger, K. (2019). Psychological assessments in legal contexts: Are courts keeping “junk science” out of the courtroom? Psychological Science in the Public Interest, 20(3), 135-164. https://doi.org/10.1177/1529100619888860
• Smalarz, Laura; Madon, Stephanie; Yang, Yueran; Guyll, Max; Buck, Sarah (2016). "The perfect match: Do criminal stereotypes bias forensic evidence analysis?". Law and Human Behavior. 40 (4): 420–429. doi:10.1037/lhb0000190. ISSN 1573-661X.
• Stern, W. (1939). "The psychology of testimony". The Journal of Abnormal and Social Psychology. 34 (1): 3–20. doi:10.1037/h0054144. ISSN 0096-851X.
• Stewart, Destin N.; Jacquin, Kristine M. (2010-11-18). "Juror Perceptions in a Rape Trial: Examining the Complainant's Ingestion of Chemical Substances Prior to Sexual Assault". Journal of Aggression, Maltreatment & Trauma. 19 (8): 853–874. doi:10.1080/10926771.2011.522951. ISSN 1092-6771.
• Viljoen, Jodi L.; Jonnson, Melissa R.; Cochrane, Dana M.; Vargen, Lee M.; Vincent, Gina M. (2019-10). "Impact of risk assessment instruments on rates of pretrial detention, postconviction placements, and release: A systematic review and meta-analysis". Law and Human Behavior. 43 (5): 397–420. doi:10.1037/lhb0000344. ISSN 1573-661X.

Afforestation

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Afforestation 

An afforestation project in Rand Wood, Lincolnshire, England

Afforestation is the establishment of a forest or stand of trees (forestation) in an area where there was no previous tree cover. Many government and non-governmental organizations directly engage in afforestation programs to create forests and increase carbon capture. Afforestation is an increasingly sought-after method to fight climate concerns, as it is known to increase the soil quality and organic carbon levels into the soil, avoiding desertification.

The rate of net forest loss decreased substantially over the period 1990–2020 due to a reduction in deforestation in some countries, plus increases in forest area in others through afforestation and the natural expansion of forests. A 2019 study of the global potential for tree restoration showed that there is space for at least 9 million km² of new forests worldwide, which is a 25% increase from current conditions. This forested area could store up to 205 gigatons of carbon or 25% of the atmosphere's current carbon pool by reducing CO₂ in the atmosphere and introducing more O₂.

Procedure

The process of afforestation begins with site selection. Several environmental factors of the site must be analyzed, including climate, soil, vegetation, and human activity. These factors will determine the quality of the site, what species of trees should be planted, and what planting method should be used.

After the forest site has been assessed, the area must be prepared for planting. Preparation can involve a variety of mechanical or chemical methods, such as chopping, mounding, bedding, herbicides, and prescribed burning. Once the site is prepared, planting can take place. One method for planting is direct seeding, which involves sowing seeds directly into the forest floor. Another is seedling planting, which is similar to direct seeding except that seedlings already have an established root system. Afforestation by cutting is an option for tree species that can reproduce asexually, where a piece of a tree stem, branch, root, or leaves can be planted onto the forest floor and sprout successfully. Sometimes special tools, such as a tree planting bar, are used to make planting of trees easier and faster.

Countries and regions

Australia

In Adelaide, South Australia (a city of 1.3 million as of June 2016), Premier Mike Rann (2002 to 2011) launched an urban forest initiative in 2003 to plant 3 million native trees and shrubs by 2014 on 300 project sites across the metro area. Thousands of Adelaide citizens have participated in community planting days on sites including parks, reserves, transport corridors, schools, water courses and coastline. Only native trees were planted to ensure genetic integrity. He said the project aimed to beautify and cool the city and make it more livable, improve air and water quality, and reduce Adelaide's greenhouse gas emissions by 600,000 tonnes of CO₂ a year.

Canada

In 2003, the government of Canada created a four-year project called the Forest 2020 Plantation Development and Assessment Initiative, which involved planting 6000 ha of fast-growing forests on non-forested lands countrywide. These plantations were used to analyze how afforestation can help to increase carbon sequestration and mitigate greenhouse gas (GHG) emissions while also considering the economic and investment attractiveness of afforestation. The results of the initiative showed that although there is not enough available land in Canada to completely offset the country's GHG emissions, afforestation can be useful mitigation technique for meeting GHG emission goals, especially until permanent, more advanced carbon storage technology becomes available.

On December 14, 2020, Canada's Minister of Natural Resources Seamus O'Regan announced the federal government's investment of $3.16 billion to plant two billion trees over the next 10 years. This plan aims to reduce greenhouse gas emissions by an estimated 12 megatonnes by 2050.

China

Strips of forest are planted along hundreds of kilometers of the Yangtze levees in Hubei province

A law promulgated in 1981 requires that every school student over the age of 11 plants at least one tree per year. As a result, China has the highest afforestation rate of any country or region in the world, with 47,000 square kilometers of afforestation in 2008. However, the forest area per capita is still far lower than the international average. According to Carbon Brief, China planted the largest amount of new forest out of any country between 1990 and 2015, facilitated by the country's Grain for Green program started in 1999, by investing more than $100 billion in afforestation programs and planting more than 35 billion trees across 12 provinces. By 2015, the amount of planted forest in China covered 79 million hectares.

From 2011 to 2016, the city Dongying in Shandong province forested over 13,800 hectares of saline soil through the Shandong Ecological Afforestation Project, which was launched with support from the World Bank. In 2017, the Saihanba Afforestation Community won the UN Champions of the Earth Award in the Inspiration and Action category for "transforming degraded land into a lush paradise".

Europe

Afforestation on former colliery land near Cwm-Hwnt, Wales

Europe has deforested the majority of its historical forests. The European Union (EU) has paid farmers for afforestation since 1990, offering grants to turn farmland into forest and payments for the management of forest. An EU program, running between 2000 and 2006, afforested more than 1,000 square kilometres of land (precise statistics not yet available). Another such program began in 2007. Europe's forests are growing by 8,000 square kilometres a year thanks to these programmes.

According to Food and Agriculture Organization statistics, Spain had the third fastest afforestation rate in Europe in the 1990-2005 period, after Iceland and Ireland. In those years, a total of 44,360 square kilometers were afforested, and the total forest cover rose from 13.5 to 17.9 million hectares. In 1990, forests covered 26.6% of the Spanish territory. As of 2007, that figure had risen to 36.6%. Spain today has the fifth largest forest area in the European Union.

In January 2013, the UK government set a target of 12% woodland cover in England by 2060, up from the then 10%. In Wales the National Assembly for Wales has set a target of 19% woodland cover, up from 15%. Government-backed initiatives such as the Woodland Carbon Code are intended to support this objective by encouraging corporations and landowners to create new woodland to offset their carbon emissions. Charitable groups such as Trees for Life (Scotland) also contribute to afforestation and reforestation efforts in the UK.

India

See also: Forestry in India

 

Afforestation in South India

23% of India is covered by forest. In 2018, the total forest and tree cover in India increased to 24.39% or 8,020. 88 km². The forests of India are grouped into 5 major categories and 16 types based on biophysical criteria. 38% of the forest is categorized as subtropical dry deciduous and 30% as tropical moist deciduous and other smaller groups. Only local species are planted in an area. Trees bearing fruits are preferred wherever possible due to their function as a food source.

In 2019, Indians Planted 220 Million trees in a Single day in the Indian state of Uttar Pradesh.

On Thursday, 29 August 2019, Prime Minister of India Mr. Narendra Modi released ₹47, 436 crores (over 6.6 Billion USD) to various states for compulsory afforestation activities. The funds can be used for treatment of catchment areas, assisted natural generation, forest management, wildlife protection and management, relocation of villages from protected areas, managing human-wildlife conflicts, training and awareness generation, supply of wood saving devices and allied activities. Increasing the tree cover would help in creating additional carbon sink to meet the nation's Intended Nationally Determined Contribution (INDC) of 2.5 to 3 billion tonnes of carbon dioxide equivalent through additional forest and tree cover by 2030 - part of India's efforts to combat climate change. The Maharashtra government planted almost 20,000,000 saplings in the entire state, and will pledge to plant another 30,000,000 next year. According to The Telegraph, the Indian government has attributed $6.2 billion for tree-planting in order to increase “forestation in line with agreements made at the Paris climate change summit in 2015.” The Indian government has also passed the CAMPA (Compensatory Afforestation Fund Management and Planning Authority) law, which will allow about 40 thousand crores rupees (almost $6 Billion) will go to Indian states for planting trees.

Iran

Fourth year of a genetically modified forest in Iran, planted by Aras GED through commercial afforestation

Iran is considered a low forest cover region of the world with present cover approximating seven percent of the land area. This is a value reduced to an estimated six million hectares of virgin forest, which includes oak, almond and pistachio. Due to soil substrates, it is difficult to achieve afforestation on a large scale compared to other temperate areas endowed with more fertile and less rocky and arid soil condition. According to the specific statistics of the Forests, Rangelands and Watershed Management Organization of Iran, every year, using appropriate methods and native tree species in each region, a lot of afforestation has been done, which has resulted in more natural stability.

Israel

JNF trees in the Negev Desert. Man-made dunes (here a liman) help keep in rainwater, creating an oasis.

 

Main article: Jewish National Fund § Afforestation

With over 240 million planted trees, Israel is one of only two countries that entered the 21st century with a net gain in the number of trees, due to massive afforestation efforts. Most Israeli forests are the product of a major afforestation campaign by the Jewish National Fund (JNF).

North Africa

Many African countries that border the Sahara desert are cooperating with the Great Green Wall project. The $8-billion project intends to restore 100 million hectares of degraded land by 2030. Also in North Africa, the Sahara Forest Project coupled with the Seawater greenhouse has been proposed. Some projects have also been launched in countries as Senegal to revert desertification. As of 2010, African leaders are discussing the combining of national resources to increase effectiveness. In addition, other projects as the Keita Project in Niger have been launched in the past, and have been able to locally revert damage done by desertification.

United States

Approximately one quarter of the United States is covered in non-protected forest. Nevertheless, areas in the US were subject to significant tree planting. In the 1800s people moving westward encountered the Great Plains – land with fertile soil, a growing population and a demand for timber but with few trees to supply it. So tree planting was encouraged along homesteads. Arbor Day was founded in 1872 by Julius Sterling Morton in Nebraska City, Nebraska. By the 1930s the Dust Bowl environmental disaster signified a reason for significant new tree cover. Public works programs under the New Deal saw the planting of 18,000 miles of windbreaks stretching from North Dakota to Texas to fight soil erosion (see Great Plains Shelterbelt).

Benefits

Afforestation boasts many climate-related benefits. Several new studies suggest that forests attract rain, which may explain why drought is occurring more frequently in certain parts of the world such as western Africa, where trees are more sparse. A 2017 study gives the first observational evidence that the southern Amazon rainforest triggers its own rainy season using water vapor from plant leaves, which then forms clouds above it. These findings help explain why deforestation in this region is linked with reduced rainfall. A 2009 study hypothesizes that forest cover plays a much greater role in determining rainfall than previously recognized. It explains how forested regions generate large-scale flows in atmospheric water vapor and further underscores the benefit of afforestation in currently barren regions of the world.

Afforestation helps to slow down global warming by reducing CO₂ in the atmosphere and introducing more O₂. Trees are carbon sinks that remove CO₂ from the atmosphere via photosynthesis and convert it into biomass.

Afforestation provides other environmental benefits, including increasing the soil quality and organic carbon levels in the soil, avoiding erosion and desertification. The planting of trees in urban areas is also able to reduce air pollution via the trees' absorption and filtration of pollutants, including carbon monoxide, sulfur dioxide, and ozone, in addition to CO₂.

Criticism

Afforestation in grasslands

Tree-planting campaigns are criticised for sometimes targeting areas where forests would not naturally occur, such as grassland and savanna biomes.

Impact on biodiversity

Afforestation can negatively affect biodiversity through increasing fragmentation and edge effects for the habitat remaining outside the planted area. New forest plantations can introduce generalist predators that would otherwise not be found in open habitat into the covered area, which could detrimentally increase predation rates on the native species of the area. A study by scientists at the British Trust for Ornithology into the decline of British populations of Eurasian curlew found that afforestation had impacted curlew populations through fragmentation of their naturally open grassland habitats and increases in generalist predators.

Surface albedo

Questions have also been raised in the scientific community regarding how global afforestation could affect the surface albedo of Earth. The canopy cover of mature trees could make the surface albedo darker, which causes more heat to be absorbed, potentially raising the temperature of the planet. This is particularly relevant in parts of the world with high levels of snow cover, due to the more significant difference in albedo between highly reflective white snow and more darker forest cover which absorbs more solar radiation.

Aerodynamics

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Aerodynamics 

A NASA wake turbulence study at Wallops Island in 1990. A vortex is created by passage of an aircraft wing, revealed by smoke. Vortices are one of the many phenomena associated with the study of aerodynamics.

Aerodynamics, from Ancient Greek: ἀήρ aero (air) + Ancient Greek: δυναμική (dynamics), is the study of the motion of air, particularly when affected by a solid object, such as an airplane wing. It involves topics covered in the field of fluid dynamics and its subfield of gas dynamics. The term aerodynamics is often used synonymously with gas dynamics, the difference being that "gas dynamics" applies to the study of the motion of all gases, and is not limited to air. The formal study of aerodynamics began in the modern sense in the eighteenth century, although observations of fundamental concepts such as aerodynamic drag were recorded much earlier. Most of the early efforts in aerodynamics were directed toward achieving heavier-than-air flight, which was first demonstrated by Otto Lilienthal in 1891. Since then, the use of aerodynamics through mathematical analysis, empirical approximations, wind tunnel experimentation, and computer simulations has formed a rational basis for the development of heavier-than-air flight and a number of other technologies. Recent work in aerodynamics has focused on issues related to compressible flow, turbulence, and boundary layers and has become increasingly computational in nature.

History

Main article: History of aerodynamics

Modern aerodynamics only dates back to the seventeenth century, but aerodynamic forces have been harnessed by humans for thousands of years in sailboats and windmills, and images and stories of flight appear throughout recorded history, such as the Ancient Greek legend of Icarus and Daedalus. Fundamental concepts of continuum, drag, and pressure gradients appear in the work of Aristotle and Archimedes.

In 1726, Sir Isaac Newton became the first person to develop a theory of air resistance, making him one of the first aerodynamicists. Dutch-Swiss mathematician Daniel Bernoulli followed in 1738 with Hydrodynamica in which he described a fundamental relationship between pressure, density, and flow velocity for incompressible flow known today as Bernoulli's principle, which provides one method for calculating aerodynamic lift. In 1757, Leonhard Euler published the more general Euler equations which could be applied to both compressible and incompressible flows. The Euler equations were extended to incorporate the effects of viscosity in the first half of the 1800s, resulting in the Navier–Stokes equations. The Navier–Stokes equations are the most general governing equations of fluid flow but are difficult to solve for the flow around all but the simplest of shapes.

A replica of the Wright brothers' wind tunnel is on display at the Virginia Air and Space Center. Wind tunnels were key in the development and validation of the laws of aerodynamics.

In 1799, Sir George Cayley became the first person to identify the four aerodynamic forces of flight (weight, lift, drag, and thrust), as well as the relationships between them, and in doing so outlined the path toward achieving heavier-than-air flight for the next century. In 1871, Francis Herbert Wenham constructed the first wind tunnel, allowing precise measurements of aerodynamic forces. Drag theories were developed by Jean le Rond d'Alembert, Gustav Kirchhoff, and Lord Rayleigh. In 1889, Charles Renard, a French aeronautical engineer, became the first person to reasonably predict the power needed for sustained flight. Otto Lilienthal, the first person to become highly successful with glider flights, was also the first to propose thin, curved airfoils that would produce high lift and low drag. Building on these developments as well as research carried out in their own wind tunnel, the Wright brothers flew the first powered airplane on December 17, 1903.

During the time of the first flights, Frederick W. Lanchester, Martin Kutta, and Nikolai Zhukovsky independently created theories that connected circulation of a fluid flow to lift. Kutta and Zhukovsky went on to develop a two-dimensional wing theory. Expanding upon the work of Lanchester, Ludwig Prandtl is credited with developing the mathematics behind thin-airfoil and lifting-line theories as well as work with boundary layers.

As aircraft speed increased designers began to encounter challenges associated with air compressibility at speeds near the speed of sound. The differences in airflow under such conditions lead to problems in aircraft control, increased drag due to shock waves, and the threat of structural failure due to aeroelastic flutter. The ratio of the flow speed to the speed of sound was named the Mach number after Ernst Mach who was one of the first to investigate the properties of the supersonic flow. Macquorn Rankine and Pierre Henri Hugoniot independently developed the theory for flow properties before and after a shock wave, while Jakob Ackeret led the initial work of calculating the lift and drag of supersonic airfoils. Theodore von Kármán and Hugh Latimer Dryden introduced the term transonic to describe flow speeds between the critical Mach number and Mach 1 where drag increases rapidly. This rapid increase in drag led aerodynamicists and aviators to disagree on whether supersonic flight was achievable until the sound barrier was broken in 1947 using the Bell X-1 aircraft.

By the time the sound barrier was broken, aerodynamicists' understanding of the subsonic and low supersonic flow had matured. The Cold War prompted the design of an ever-evolving line of high-performance aircraft. Computational fluid dynamics began as an effort to solve for flow properties around complex objects and has rapidly grown to the point where entire aircraft can be designed using computer software, with wind-tunnel tests followed by flight tests to confirm the computer predictions. Understanding of supersonic and hypersonic aerodynamics has matured since the 1960s, and the goals of aerodynamicists have shifted from the behaviour of fluid flow to the engineering of a vehicle such that it interacts predictably with the fluid flow. Designing aircraft for supersonic and hypersonic conditions, as well as the desire to improve the aerodynamic efficiency of current aircraft and propulsion systems, continues to motivate new research in aerodynamics, while work continues to be done on important problems in basic aerodynamic theory related to flow turbulence and the existence and uniqueness of analytical solutions to the Navier–Stokes equations.

Fundamental concepts

Forces of flight on a powered aircraft in unaccelerated level flight

Understanding the motion of air around an object (often called a flow field) enables the calculation of forces and moments acting on the object. In many aerodynamics problems, the forces of interest are the fundamental forces of flight: lift, drag, thrust, and weight. Of these, lift and drag are aerodynamic forces, i.e. forces due to air flow over a solid body. Calculation of these quantities is often founded upon the assumption that the flow field behaves as a continuum. Continuum flow fields are characterized by properties such as flow velocity, pressure, density, and temperature, which may be functions of position and time. These properties may be directly or indirectly measured in aerodynamics experiments or calculated starting with the equations for conservation of mass, momentum, and energy in air flows. Density, flow velocity, and an additional property, viscosity, are used to classify flow fields.

Flow classification

Flow velocity is used to classify flows according to speed regime. Subsonic flows are flow fields in which the air speed field is always below the local speed of sound. Transonic flows include both regions of subsonic flow and regions in which the local flow speed is greater than the local speed of sound. Supersonic flows are defined to be flows in which the flow speed is greater than the speed of sound everywhere. A fourth classification, hypersonic flow, refers to flows where the flow speed is much greater than the speed of sound. Aerodynamicists disagree on the precise definition of hypersonic flow.

Compressible flow accounts for varying density within the flow. Subsonic flows are often idealized as incompressible, i.e. the density is assumed to be constant. Transonic and supersonic flows are compressible, and calculations that neglect the changes of density in these flow fields will yield inaccurate results.

Viscosity is associated with the frictional forces in a flow. In some flow fields, viscous effects are very small, and approximate solutions may safely neglect viscous effects. These approximations are called inviscid flows. Flows for which viscosity is not neglected are called viscous flows. Finally, aerodynamic problems may also be classified by the flow environment. External aerodynamics is the study of flow around solid objects of various shapes (e.g. around an airplane wing), while internal aerodynamics is the study of flow through passages inside solid objects (e.g. through a jet engine).

Continuum assumption

Unlike liquids and solids, gases are composed of discrete molecules which occupy only a small fraction of the volume filled by the gas. On a molecular level, flow fields are made up of the collisions of many individual of gas molecules between themselves and with solid surfaces. However, in most aerodynamics applications, the discrete molecular nature of gases is ignored, and the flow field is assumed to behave as a continuum. This assumption allows fluid properties such as density and flow velocity to be defined everywhere within the flow.

The validity of the continuum assumption is dependent on the density of the gas and the application in question. For the continuum assumption to be valid, the mean free path length must be much smaller than the length scale of the application in question. For example, many aerodynamics applications deal with aircraft flying in atmospheric conditions, where the mean free path length is on the order of micrometers and where the body is orders of magnitude larger. In these cases, the length scale of the aircraft ranges from a few meters to a few tens of meters, which is much larger than the mean free path length. For such applications, the continuum assumption is reasonable. The continuum assumption is less valid for extremely low-density flows, such as those encountered by vehicles at very high altitudes (e.g. 300,000 ft/90 km) or satellites in Low Earth orbit. In those cases, statistical mechanics is a more accurate method of solving the problem than is continuum aerodynamics. The Knudsen number can be used to guide the choice between statistical mechanics and the continuous formulation of aerodynamics.

Conservation laws

The assumption of a fluid continuum allows problems in aerodynamics to be solved using fluid dynamics conservation laws. Three conservation principles are used:

Conservation of mass

Conservation of mass requires that mass is neither created nor destroyed within a flow; the mathematical formulation of this principle is known as the mass continuity equation.

Conservation of momentum

The mathematical formulation of this principle can be considered an application of Newton's Second Law. Momentum within a flow is only changed by external forces, which may include both surface forces, such as viscous (frictional) forces, and body forces, such as weight. The momentum conservation principle may be expressed as either a vector equation or separated into a set of three scalar equations (x,y,z components).

Conservation of energy

The energy conservation equation states that energy is neither created nor destroyed within a flow, and that any addition or subtraction of energy to a volume in the flow is caused by heat transfer, or by work into and out of the region of interest.

Together, these equations are known as the Navier–Stokes equations, although some authors define the term to only include the momentum equation(s). The Navier–Stokes equations have no known analytical solution and are solved in modern aerodynamics using computational techniques. Because computational methods using high speed computers were not historically available and the high computational cost of solving these complex equations now that they are available, simplifications of the Navier–Stokes equations have been and continue to be employed. The Euler equations are a set of similar conservation equations which neglect viscosity and may be used in cases where the effect of viscosity is expected to be small. Further simplifications lead to Laplace's equation and potential flow theory. Additionally, Bernoulli's equation is a solution in one dimension to both the momentum and energy conservation equations.

The ideal gas law or another such equation of state is often used in conjunction with these equations to form a determined system that allows the solution for the unknown variables.

Branches of aerodynamics

computational modelling

Aerodynamic problems are classified by the flow environment or properties of the flow, including flow speed, compressibility, and viscosity. External aerodynamics is the study of flow around solid objects of various shapes. Evaluating the lift and drag on an airplane or the shock waves that form in front of the nose of a rocket are examples of external aerodynamics. Internal aerodynamics is the study of flow through passages in solid objects. For instance, internal aerodynamics encompasses the study of the airflow through a jet engine or through an air conditioning pipe.

Aerodynamic problems can also be classified according to whether the flow speed is below, near or above the speed of sound. A problem is called subsonic if all the speeds in the problem are less than the speed of sound, transonic if speeds both below and above the speed of sound are present (normally when the characteristic speed is approximately the speed of sound), supersonic when the characteristic flow speed is greater than the speed of sound, and hypersonic when the flow speed is much greater than the speed of sound. Aerodynamicists disagree over the precise definition of hypersonic flow; a rough definition considers flows with Mach numbers above 5 to be hypersonic.

The influence of viscosity on the flow dictates a third classification. Some problems may encounter only very small viscous effects, in which case viscosity can be considered to be negligible. The approximations to these problems are called inviscid flows. Flows for which viscosity cannot be neglected are called viscous flows.

Incompressible aerodynamics

Further information: incompressible flow

An incompressible flow is a flow in which density is constant in both time and space. Although all real fluids are compressible, a flow is often approximated as incompressible if the effect of the density changes cause only small changes to the calculated results. This is more likely to be true when the flow speeds are significantly lower than the speed of sound. Effects of compressibility are more significant at speeds close to or above the speed of sound. The Mach number is used to evaluate whether the incompressibility can be assumed, otherwise the effects of compressibility must be included.

Subsonic flow

Subsonic (or low-speed) aerodynamics describes fluid motion in flows which are much lower than the speed of sound everywhere in the flow. There are several branches of subsonic flow but one special case arises when the flow is inviscid, incompressible and irrotational. This case is called potential flow and allows the differential equations that describe the flow to be a simplified version of the equations of fluid dynamics, thus making available to the aerodynamicist a range of quick and easy solutions.

In solving a subsonic problem, one decision to be made by the aerodynamicist is whether to incorporate the effects of compressibility. Compressibility is a description of the amount of change of density in the flow. When the effects of compressibility on the solution are small, the assumption that density is constant may be made. The problem is then an incompressible low-speed aerodynamics problem. When the density is allowed to vary, the flow is called compressible. In air, compressibility effects are usually ignored when the Mach number in the flow does not exceed 0.3 (about 335 feet (102 m) per second or 228 miles (366 km) per hour at 60 °F (16 °C)). Above Mach 0.3, the problem flow should be described using compressible aerodynamics.

Compressible aerodynamics

Main article: Compressible flow

According to the theory of aerodynamics, a flow is considered to be compressible if the density changes along a streamline. This means that – unlike incompressible flow – changes in density are considered. In general, this is the case where the Mach number in part or all of the flow exceeds 0.3. The Mach 0.3 value is rather arbitrary, but it is used because gas flows with a Mach number below that value demonstrate changes in density of less than 5%. Furthermore, that maximum 5% density change occurs at the stagnation point (the point on the object where flow speed is zero), while the density changes around the rest of the object will be significantly lower. Transonic, supersonic, and hypersonic flows are all compressible flows.

Transonic flow

Main article: Transonic

The term Transonic refers to a range of flow velocities just below and above the local speed of sound (generally taken as Mach 0.8–1.2). It is defined as the range of speeds between the critical Mach number, when some parts of the airflow over an aircraft become supersonic, and a higher speed, typically near Mach 1.2, when all of the airflow is supersonic. Between these speeds, some of the airflow is supersonic, while some of the airflow is not supersonic.

Supersonic flow

Main article: Supersonic

Supersonic aerodynamic problems are those involving flow speeds greater than the speed of sound. Calculating the lift on the Concorde during cruise can be an example of a supersonic aerodynamic problem.

Supersonic flow behaves very differently from subsonic flow. Fluids react to differences in pressure; pressure changes are how a fluid is "told" to respond to its environment. Therefore, since sound is, in fact, an infinitesimal pressure difference propagating through a fluid, the speed of sound in that fluid can be considered the fastest speed that "information" can travel in the flow. This difference most obviously manifests itself in the case of a fluid striking an object. In front of that object, the fluid builds up a stagnation pressure as impact with the object brings the moving fluid to rest. In fluid traveling at subsonic speed, this pressure disturbance can propagate upstream, changing the flow pattern ahead of the object and giving the impression that the fluid "knows" the object is there by seemingly adjusting its movement and is flowing around it. In a supersonic flow, however, the pressure disturbance cannot propagate upstream. Thus, when the fluid finally reaches the object it strikes it and the fluid is forced to change its properties – temperature, density, pressure, and Mach number—in an extremely violent and irreversible fashion called a shock wave. The presence of shock waves, along with the compressibility effects of high-flow velocity (see Reynolds number) fluids, is the central difference between the supersonic and subsonic aerodynamics regimes.

Hypersonic flow

Main article: Hypersonic

In aerodynamics, hypersonic speeds are speeds that are highly supersonic. In the 1970s, the term generally came to refer to speeds of Mach 5 (5 times the speed of sound) and above. The hypersonic regime is a subset of the supersonic regime. Hypersonic flow is characterized by high temperature flow behind a shock wave, viscous interaction, and chemical dissociation of gas.

Associated terminology

Different types flow analysis around an airfoil:

  Potential flow theory

  Boundary layer flow theory

  Turbulent wake analysis

The incompressible and compressible flow regimes produce many associated phenomena, such as boundary layers and turbulence.

Boundary layers

Main article: Boundary layer

The concept of a boundary layer is important in many problems in aerodynamics. The viscosity and fluid friction in the air is approximated as being significant only in this thin layer. This assumption makes the description of such aerodynamics much more tractable mathematically.

Turbulence

Main article: Turbulence

In aerodynamics, turbulence is characterized by chaotic property changes in the flow. These include low momentum diffusion, high momentum convection, and rapid variation of pressure and flow velocity in space and time. Flow that is not turbulent is called laminar flow.

Aerodynamics in other fields

Engineering design

Further information: Automotive aerodynamics

Aerodynamics is a significant element of vehicle design, including road cars and trucks where the main goal is to reduce the vehicle drag coefficient, and racing cars, where in addition to reducing drag the goal is also to increase the overall level of downforce. Aerodynamics is also important in the prediction of forces and moments acting on sailing vessels. It is used in the design of mechanical components such as hard drive heads. Structural engineers resort to aerodynamics, and particularly aeroelasticity, when calculating wind loads in the design of large buildings, bridges, and wind turbines

The aerodynamics of internal passages is important in heating/ventilation, gas piping, and in automotive engines where detailed flow patterns strongly affect the performance of the engine.

Environmental design

Urban aerodynamics are studied by town planners and designers seeking to improve amenity in outdoor spaces, or in creating urban microclimates to reduce the effects of urban pollution. The field of environmental aerodynamics describes ways in which atmospheric circulation and flight mechanics affect ecosystems.

Aerodynamic equations are used in numerical weather prediction.

Ball-control in sports

Sports in which aerodynamics are of crucial importance include soccer, table tennis, cricket, baseball, and golf, in which most players can control the trajectory of the ball using the "Magnus effect".