In compressible fluid dynamics, impact pressure (dynamic pressure) is the difference between total pressure (also known as pitot pressure or stagnation pressure) and static pressure.
[1][2] In aerodynamics notation, this quantity is denoted as
When input to an airspeed indicator, impact pressure is used to provide a calibrated airspeed reading.
An air data computer with inputs of pitot and static pressures is able to provide a Mach number and, if static temperature is known, true airspeed.
[citation needed] Some authors in the field of compressible flows use the term dynamic pressure or compressible dynamic pressure instead of impact pressure.
[3][4] In isentropic flow the ratio of total pressure to static pressure is given by:[3]
γ − 1
γ
γ − 1
is total pressure
is static pressure
γ
is the ratio of specific heats
is the freestream Mach number
Expressing the incompressible dynamic pressure as
and expanding by the binomial series gives:
is dynamic pressure