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 or .

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]

Isentropic flowEdit

In isentropic flow the ratio of total pressure to static pressure is given by:[3]

 

where:

  is total pressure

  is static pressure

  is the ratio of specific heats

  is the freestream Mach number


Taking   to be 1.4, and since  


 


Expressing the incompressible dynamic pressure as   and expanding by the binomial series gives:


 

where:

  is dynamic pressure

See alsoEdit

ReferencesEdit

  1. ^ DoD and NATO definition of impact pressure Retrieved on 2008-10-01
  2. ^ The Free Dictionary Retrieved on 2008-10-01
  3. ^ a b L. J. Clancy (1975) Aerodynamics, Section 3.12 and 3.13
  4. ^ "the dynamic pressure is equal to half rho vee squared only in incompressible flow."
    Houghton, E.L. and Carpenter, P.W. (1993), Aerodynamics for Engineering Students, Section 2.3.1