Ideal-gas sound speed

Purpose

The isentropic sound speed used by Roe eigenvalues and spectral radii is recovered from total enthalpy after removing kinetic energy.

Formula

\[c = \sqrt{(\gamma-1)\left(H-\frac{1}{2}|u|^{2}\right)}\]

Source map

  • IdealGasSoundSpeed in NsInvFluxPolicy

  • Upstream: IdealGasStaticEnthalpy, TotalEnthalpy

  • Downstream: RoeAbsoluteEigenvalues, inviscid spectral radius

  • Tests: tests/solver/inv_flux_policy_test.cpp

  • Theory table: tools/verification/data/ideal_gas_sound_speed_theory.csv

  • Contract Workbench id: ideal_gas_sound_speed

Ideal-gas sound speed vs total enthalpy

What this proves / does not prove

Proves: sound-speed algebra matches the pure API on sample states.

Does not prove: real-gas thermodynamics or assembled flux residual.