Investigation of feedback loop in the impinging jet

It is important to take noise control of impinging jetsin many engineering fields, such as a short take-off and vertical landing(SVTOL) aircraft as well as air nozzle. In general, the impinging jet noiseis associated with the relationship between the impinging tone and the scaleof vortex structure, and the propagating direction of feedback waves. In thepresent study, the propagation direction of impinging tone was investigatedwith wavelet analysis and acoustic analogy. The velocity field of impingingjet was obtained by Particle Image Velocimetry (PIV) technique anddecomposed by means of biorthogonal wavelet transform. The frequencydistribution of discrete tone was obtained from its noise field. The resultsshow that large-scale structure can be viewed as ``coustic source'' ofdiscrete tone. Moreover, the direction of upstream-propagating feedbackwaves is about 60^\circ oriented from the impinging plane and agrees withHo's experimental results.