EXPERIMENTS ON RESPONSE OF IMPINGING-JET EDGE TONE TO EDGE MISALIGNMENT AND SPANWISE COHERENCE OF THE JET

The edge tone generated by a two-dimensional jet impinging on a circul ar cylinder was modulated by; first, changing the normal distance betw een the axis of the jet and that of the cylinder Delta y, second, incl ining the axis of the cylinder with respect to the span of the jet by an angle theta(j) and third, reducing the spanwise coherence of the je t by the use of a thin circular rod (attached to the exit of the nozzl e) whose axis was normal to the span of the jet. The normal distance D elta y, the angle theta and the diameter and spanwise position of the rod were systematically changed. There existed a critical value of the se parameters beyond which the regular edge tone of high amplitude was replaced by an irregular sound of a much lower level. The critical va lues were functions of the jet velocity. At the critical values of the parameters the regular edge tone and the irregular sound switched ran domly with an average interval which was much greater than the period of the regular edge tone. (C) 1995 Academic Press Limited