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# question in direction of flow in steady frame

Posted on 2014-02-21

I am looking at a solution of an engineering problem. There is a blast wave that moves through standard air conditions. The wave passes a stationary observer on the ground.

The problems asks to calculate mach number and direction of flow

so...

It calculates Mach 1 = 10 , Mach 2 = 0.387

then finds u1 = 3557 , u2 = 0.38757

then it states : for stationary reference frame

V2 = u1 - u2 = 2935.1

calculates M2 = v2/a2 = 1.8270

thus V2 is directed to shock front

my question is : what is the reasoning behind this assumption that v2 is directed to shock front ?

Any input would be appreciated.