Shock Tube Technique Studies in Detonation

Up to this time, the pressure thruout the region from the piston to the advancing front remains constant. Even after the piston is stopped the front continues to advance at its previous supersonic velocity and the pressure remains at this constant value for a considerable distance behind the front. However, the movement away of the material immediately ahead of the piston creates a rarefaction, for there is nothing to take the place of removed air. The pressure within this rarefaction zone will fall below the original pressure and will even approach.a vacuum in some cases. While the shock front continues to advance, the rarefaction wave follows some distance behind. It has been shown that in an inert medium, such. a rarefaction wave will always advance faster than the original shock front and is bound to overtake 

Morrison (Ref 1, pp 38-42) described a shock tube (See Fig 1) containing inside a piston which separates two gases of two different states. One section of the tube is closed from the outside forming a reservoir. Assuming that the gas to the left of piston is at a higher pressure than the gas to the right of it, let the piston (starting 

FIG 2 TIME-DISTANCE PLOT SHOWING THE LOCATION OF THE RAREFACTION WAVE, PISTON, AND SHOCK WAVE 

The flow process may then be broken into two problems 1) a study of the flow to the right of piston and 2) a study of the flow to the left of the piston 

If the piston is replaced by a diaphragm and the diaphragm is ruptured, the problems would be analogous the only difference being that the pressures and velocities are continuous across the piston 

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