Prandtl–Glauert Rule

A linearized compressibility correction that approximates subsonic aerodynamic pressure and force coefficients by scaling incompressible (low‑Mach) results with a factor 1/√(1 − M∞^2) (the Prandtl–Glauert factor), valid for small disturbances, thin profiles and steady subsonic free streams away from transonic nonlinearities.