Frequently Asked Question

Density, viscosity, conductivity, and specific heat must be mutually consistent with the selected thermodynamic state. Temperature-dependent properties can couple thermal and momentum predictions strongly.

Use one documented property source and state interpolation ranges. If a property is extrapolated beyond its valid range, quantify its effect on the reported output.

Compressibility and waves

Compressibility matters when density changes influence continuity, momentum, energy, or wave propagation. Mach number compares flow speed with acoustic speed, while temperature and pressure are coupled through thermodynamic closure. Shocks and expansions create strong gradients and require conservation-consistent treatment. Static and total quantities must never be mixed without stating the reference frame and thermodynamic definition.

M is Mach number, U is speed, a is acoustic speed, γ is heat-capacity ratio, R is the specific gas constant, and T is absolute temperature.

Worked example

At U = 340 m/s and a = 340 m/s, M = 1.0. A temperature change alters acoustic speed and therefore the local Mach number even if velocity is unchanged. Use absolute temperature and properties consistent with the gas composition.

Check: compare total-pressure loss, static-pressure recovery, shock position, and energy conservation using consistent planes.

Engineering check

For Thermodynamic and Transport-Property Consistency, maintain traceability from requirement to risk, design output, evidence, and approval. Record the configuration, acceptance criterion, test or analysis conditions, open actions, and residual risk. A method is not complete when the document is filled in; it is complete when the evidence supports the decision and affected controls are updated.