Stagnation pressure
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Stagnation pressure is the pressure at a stagnation point in a fluid flow, where the kinetic energy is converted into pressure energy.
It is the pressure a fluid retains when brought to rest isentropically from mach number M.
<math>\frac{p_t}{p} = \left(1 + \frac{\gamma -1}{2} M^2\right)^{\frac{\gamma}{\gamma-1}}\, </math>
or, assuming an isentropic process, the stagnation pressure can be calculated from the ratio of stagnation temperature to static temperature:
<math>\frac{p_t}{p} = \left(\frac{T_t}{T}\right)^{\frac{\gamma}{\gamma-1}}\,</math>
where:
<math>p_t =\,</math> stagnation (or total) pressure
<math>p =\,</math> static pressure
<math>T_t =\,</math> stagnation (or total) temperature in kelvins
<math>T =\,</math> static temperature in kelvins
<math>\gamma\ =\,</math> ratio of specific heats
The above derivation holds only for the case when the fluid is assumed to be calorically perfect. For such fluids, specific heats and <math>\gamma</math> are assumed to be constant and invariant with temperature (See also, a thermally perfect fluid).
Stagnation quantities (e.g. stagnation temperature, stagnation pressure) are frequently used in jet engine performance calculations.
Pitot tubes are used to measure stagnation (or total) pressure. A combined pitot/static tube is used on aircraft to determine flight speed..
