2001 Volume 21 Issue 1Supplement Pages 97-100
Feedback mechanism of self-sustained oscillation in supersonic impinging jets is studied experimentally by using a laser-induced fluorescence (LIF) technique. Phase velocities of disturbances in the flow field are obtained from a time-dependent cross-correlation function between a pressure sensor signal at a reference point and the LIF signal. A feature of disturbance propagation can be visualized by drawing maps for the cross-correlation coefficients on a plane at successive delay-times and making an animation. The discrete frequencies appeared near the neutral wave frequencies proposed by Tam and axisymmetric and helical models of the neutral wave were observed corresponding to his theory. Although the neutral waves propagate upstream both outside and inside the jet, the feedback loop is mainly accomplished by the outside propagating waves.
