PRESSURE FIELD AROUND A RECTANGULAR SUPERSONIC JET IN SCREECH

Supersonic jet screech generated by a rectangular nozzle with a pair o f side walls added is studied both experimentally and numerically, A d etailed observation of screech phenomena contributes to an understandi ng of the mechanism of sound generation, The numerical simulation show s that computational aeroacoustics is effective for strongly coupled f low acoustic problems such as screech, Flow visualization by an acoust ically triggered pulse laser schlieren system clearly shows the dynami c motion of the third shock cell in the flapping mode, A traveling sho ck is found to exist in the third shock cell, and the sound is generat ed at the moment when the traveling shock coalesces into the end shock of the third shock cell, The instantaneous pressure distribution on t he side wall shows that a pressure wave convectively propagates along the shear layer in the near field of the jet, while it propagates acou stically in the vertical direction away from the jet, Numerical simula tion shows similar aspects of screech to those obtained in the experim ent: the screech frequency the flowfield, the fluctuating pressure dis tribution, etc, The calculated acoustic intensity shows that the acous tic energy is radiated at the end of the compression portion of each s hock cell, The source of the first shock cell seems to supply the acou stic energy to its own shear layer to sustain the oscillation, It is a lso shown that the dimple spots observed in the isoamplitude contours of the screech sound pressure are a result of the interaction between discrete sources located at the end of each shock cell.