A Study of Area Change Near the Diaphragm of a Shock Tube

The performance of a shock tube with area change near the diaphragm has been calculated for the high shock speed case by previous authors. This report extends the ideal theory calculations to include the whole shock speed range and all possible area changes near the diaphragm. Simple calculation procedures are presented and the practical applications of this type of area change are discussed. Experimental measurements show excellent agreement with the theory except for the intermediate shock speed range where a non-steady secondary shock wave is predicted. Here not only is the agreement with the basic performance curves marginal, but detailed observations revealed that no secondary normal shock is present! A new model is devised to explain these discrepancies. This new model takes frictional effects into account and shows promise of being useful for other shock tube problems