Abstract:
The phase criterion of the feedback cycle of low-speed edgetones has been obtained using the jet--edge interaction model in which the reaction of the wedge to the impinging jet is modeled by an array of dipoles. The edgetone is produced by the feedback loop between the downstream-convected unstable flow issued from the nozzle and the upstream-propagating sonic wave due to the wedge reaction. By estimating the phase difference between the downstream flow and the upstream wave, and by imposing the phase-locking condition at the nozzle lip, it is found that the phase factor should be p=-1/4 in the feedback relation h/(Lambda)+h/(lambda)=n+p, where h is the stand-off distance, (Lambda) and (lambda) are the wavelengths of downstream- and upstream-propagating disturbances, respectively, and n is a stage number for the ladder-like characteristics of frequency. The proposed criterion p=-1/4 is just the opposite, in phase, to p=1/4 that has been regarded as an established characteristic of edgetones. However, p=-1/4 is verified substantially in comparison with available experimental data and found to be effective up to a wedge angle of 90(degrees). [Work supported by KOSEF.]