OSCILLATION MODES OF LAVAL NOZZLE-FLOW

Experimental investigations of Laval nozzle flow show for relatively l ow supply to exit pressure ratios, which correspond to shock wave posi tions close to the nozzle throat, three different, oscillatory instabi lities. (i) Shock pattern oscillations where the root of a lambda-like shock front remains nearly in constant position, but where the propor tion between the normal part and the oblique part of the shock changes periodically. (ii) Shock wave and separation bubble oscillations wher e the motion of the shock wave is accompanied by displacements of the separation bubble. (iii) Flow rate oscillations where the shock waves leave periodically through the nozzle throat in upstream direction.