Weak-oblique-shock deflection
= Weak-oblique-shock deflection
If $p_2/p_1=1+\epsilon$ with $0<\epsilon\ll1$ and the upstream Mach number is $M_1>1$, the shock angle is the Mach angle to leading order and the flow deflection is
$$
\theta\simeq\frac{\epsilon}{\gamma}
\frac{\sqrt{M_1^2-1}}{M_1^2}.
$$
The normal speed decreases, so the downstream flow turns toward the shock front.