Summary http://edugen.wiley.com/edugen/courses/crs2436/crowe9771/crowe9771...
Summary
The speed of sound is the speed at which an infinitesimal pressure disturbance travels through a fluid. The speed
of sound in an ideal gas is
where k is the ratio of specific heats, R is the gas constant, and T is the absolute temperature. The Mach number
is defined as
Compressible flows are classified as
In general, if the Mach number is less than 0.3, a steady flow can be regarded as incompressible.
For an adiabatic flow (no heat transfer), the temperature varies along a streamline according to
where Tt, the total temperature, is the temperature attained if the flow is decelerated to zero velocity. If the flow
is isentropic, the pressure varies along a streamline as
where pt is the total pressure, the pressure achieved if the flow is decelerated to zero velocity isentropically.
A normal shock wave is a narrow region where a supersonic flow is decelerated to a subsonic flow with an
attendant rise in pressure, temperature, and density. The total temperature does not change through a shock
wave, but the total pressure decreases. The shock wave is a nonisentropic process and can only occur in
supersonic flows.
A Laval nozzle is a duct with a converging and expanding area that is used to accelerate a compressible fluid to
supersonic speeds. Sonic flow can occur only at the nozzle throat (minimum area). The ratio of the area at a
location in the nozzle to the throat area, A/A*, is a function of the local Mach number and the ratio of specific
heats. The flow rate through a Laval nozzle is given by
A Laval nozzle is classified by comparing the pressure at the exit, pe, for supersonic flow in the nozzle with the
back (ambient) pressure, pb.
Shock waves occur in overexpanded nozzles, yielding a subsonic flow at the exit.
A truncated nozzle is a Laval nozzle terminated at the throat typically used for mass flow measurement.
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Summary http://edugen.wiley.com/edugen/courses/crs2436/crowe9771/crowe9771...
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