OSCILLATIONS OF A MODERATELY UNDEREXPANDED CHOKED JET IMPINGING UPON A FLAT-PLATE

The oscillation of a moderately underexpanded choked jet impinging upo n a flat plate is investigated both analytically and numerically. The feedback mechanism between oscillations of the standoff-shock and the plate is clarified. Pressure waves produced by the motion of the shock are reflected by the plate. In addition, oscillations in the shock po sition lead to downstream entropy fluctuations, which generate pressur e waves as' they are convected through the stagnation flow near the pl ate. A linear stability analysis is used to investigate the stability threshold and frequencies of oscillation, as a function of jet pressur e ratio and nozzle-to-plate distance. The analytical predictions are c ompared to results from a numerical simulation and to the experimental data of Powell (1988) and Morch (1963, 1964).