Critical speed of a polytropic flow
= Critical speed of a polytropic flow
{title2=$c_{\rm cr}$}
For a steady polytropic streamline with Bernoulli function $C_B$, the critical speed is the sound speed at which the scalar mass flux $\rho u$ is maximal. It satisfies
$$
c_{\rm cr}^2=\frac{2(\gamma-1)}{\gamma+1}C_B.
$$