I am interested in knowing if a nozzle (Convegent-Divergent) is choked (sonic state at the throat).
I have read that the nozzle is choked if :
the static pressure $p_t$ at the throat is equal to the critical pressure $p_*$, where $p_*$ depends on the upstream total pressure $p_{i_0}$ : $p_* = p_{i_0}(\frac{2}{\gamma +1})^{\frac{\gamma}{\gamma -1}}$
However, usually we don't have the throat pressure. So I have found that we can verify whether the throat is choked if :
$\frac{p_{i_0}}{p_{amb}} > (\frac{\gamma +1}{2})^{\frac{\gamma}{\gamma -1}}$
$p_{amb}$ is the ambiant pressure outside the nozzle (which is not equal to the exit nozzle pressure in general)
But I don't understand why, if we verify this inequality, the nozzle is indeed choked. (The critical pressure does not appear)
