Face Mach number

Purpose

The relative face Mach number is the ratio of relative normal velocity to local sound speed. It drives AUSM-type mass and pressure split functions.

Formula

\[M = \frac{v_n}{c}\]

Source map

FaceMachNumber in NsInvFluxPolicy
Consumers: AUSM paths in NsInvFlux
Tests: tests/solver/inv_flux_policy_test.cpp
Theory table: tools/verification/data/face_mach_number_theory.csv
Contract Workbench id: face_mach_number

Face Mach number vs relative normal velocity

What this proves / does not prove

Proves: (M=v_n/c) matches the pure API on a velocity grid.

Does not prove: AUSM flux accuracy or full inviscid residual.

References

Liou, AUSM-family schemes (face Mach as primary interface quantity).
Related: AUSM Mach and pressure split polynomials (when present), Ideal-gas sound speed from pressure.