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GRA October 15, 2006 08:03

Will compression waves overtake a moving shock?
The scenario is like this.

An unsteady shock is discharged from a shock tube and it is followed by a starting vortex pair and a secondary shock wave. The whole thing is created due to the movement of a piston inside the shock tube. The secondary shock wave is preceded by a supersonic jet which is continuously influenced by the compression waves generated by the movement of the piston. Well, now the system consists of a primary shock wave (blast wave), a secondary shock wave behind that and an expanding supersonic jet behind the seconday shock wave. Is it possible that the compression waves generated by the piston can overtake the secondary shock wave?

thanx for reading


Mani October 17, 2006 09:45

Re: Will compression waves overtake a moving shock
I doubt it. If the secondary shock is faster than the primary (I assume so), it will catch up and both shock will merge to form a stronger shock. Much like the evolution of any moving shock could be described as a merger of many weak compression waves, catching up with each other. Is this a quiz? :)

GRA October 19, 2006 00:24

Re: Will compression waves overtake a moving shock
Thnx Mr.Mani for your suggestion.

Infact, I have been trying to figure out the underlying physics in a such a situation. You are correct in the sense that a moving shock wave is formed due to coalescing compression waves like the ones which are produced consequent to a diaphragm rupture in a shock tube. Here the situation is rather different as an accelerating piston is continuosly generating compression waves behind the moving shock wave. Moreover, a jet flow is also developed in between the moving shock and the piston. In such a situation, my doubt was whether either the gas in the jet or compression waves traveling through the jet would overtake the moving shock. Now my problem is solved as it is understood that the compression waves will strengethen the moving shock and it achieves its full strength and is overtaken by the supersonic jet before having diffracted by the moving piston..

Thank you for finding time to answer my doubt.

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