不足膨張衝突噴流の振動現象

抄録

Self-excited oscillation of an underexpanded jet issuing from a circular nozzle and impinging perpendicularly on a flat plate is analyzed numerically using a TVD scheme. With some nozzle-plate spacings, simple patterns of the oscillation of the flow fields are obtained numerically, and their pressure histories at the center of the plate also show simple wave patterns with a certain amplitude of the pressure. Their amplitudes increase with increase in the nozzle-plate spacing, and a dominant frequency of about 20-30 kHz is obtained by FFT analysis of those pressure histories. The numerical results agree with the experimental data. Such self-excited oscillation seem to be related to the noise of the jet. The amplitude of the pressure history is considered to depend on the area of the compressive region upstream of the plate shock. It is also found that the pressure wave which is generated near the impinging region travels toward the nozzle wall in the air surrounding the jet, which causes the whole jet to oscillate.