Question

Which of the following is incorrect for a normal shock wave?

(a) M1=1 then M2=1

(b) M1 > then M2 > 1

(c) M\(_1^*\)=1→M\(_2^*\)=1

(d) M1→∞ then M2=finite value

I had been asked this question in homework.

Asked question is from Flow Compressible in chapter Normal Shock Waves of Aerodynamics

Answer 1

Right option is (b) M1 > then M2 > 1

Easiest explanation: For a normal shock wave, the upstream and downstream Mach numbers are related irrespective of the other parameters for a particular flow. According to the relation, M1=1 then M2=1 and  M1 > then  M2 < 1, since normal shock wave compresses the flow. Also, by Prandtl relation when M\(_1^*\)=1→M\(_2^*\)=1 and when  M1→∞ then M2 takes a finite value.