ELSEVIER The Feedback Loop in Impinging Two-Dimensional High-Subsonic and Supersonic Jets K. Hour igan

• The instabilities in a supersonic impinging jet are investigated by solving the two-dimensional Euler equations using the piecewise parabolic method (PPM) and Roe's linearized Riemann solver. The predicted shock cell spacing agrees well with the observed and theoretical values. The frequency and nature of the dominant instabilities are found to be a function of the impingement distance. Two instability modes are possible: a symmetric (or varicose) mode and an asymmetric (or sinuous) mode. For two given jet exit Mach numbers (M = 0.98 and 1.29), the energy in, and frequency of, these modes are functions of impingement distance, leading to an integral staging due to an acoustic feedback loop. The predicted frequencies of the funda-mental symmetric and asymmetric nstabilities agree with the theoretically allowed values. The staging of predicted frequencies that occurs in experi-mental work is also predicted