Density changes matter when Mach number exceeds about 0.3.
When Mach number exceeds about 0.3, density changes become significant. Flow properties vary with Mach; stagnation properties T₀=T(1+(γ-1)M²/2). Includes subsonic, transonic, supersonic and hypersonic regimes with shock waves and expansion fans.
At Mach 2, air's stagnation temperature is 1.8× static temperature.
Compressible effects matter at high speed, so engineers must know when density changes can be ignored and when they must be included.
Density changes matter when Mach number exceeds about 0.3.
Compressible effects matter at high speed, so engineers must know when density changes can be ignored and when they must be included.
Typically below Mach 0.3, where density changes are small enough that incompressible flow gives acceptable accuracy.
Pressure waves cannot move ahead of the flow fast enough at high speed, so density changes and shocks appear.
Typical applications include deciding whether a wind tunnel must account for compressibility at a given speed, designing a high-speed aircraft inlet and checking compressible losses in a gas pipeline at high velocity.
Study "Hydraulic jump" first (topic 75 of 105 in Thermodynamics & Fluids). It covers the groundwork this topic builds on.
Choked flow. Area-velocity relation. Compressibility corrections.
At Mach 2, air's stagnation temperature is 1.8× static temperature.
The next topic is "Mach number and speed of sound", which builds directly on this one.
It is classed as Advanced in Thermodynamics & Fluids (topic 76 of 105). It is an advanced topic. It assumes you are comfortable with the intermediate topics in Thermodynamics & Fluids.
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