Choked-jet edge-tone experiments, Continued.

Abstract

Edge tones occur continuously from somewhat below choking, at pressure ratio R=1.89, to somewhat above R=4.1, for a 17.7-×3.7-mm nozzle and 8° wedge. In marked contrast to the classical edge tone, the behavior is complex with varying characteristics. For 2.22≤R≤2.43 and edge-to-nozzle distance 2≤h/δ≤17 distance (δ=3.7 mm) many scattered edge tones occur. Around R=2.50 with 3.1≤h/δ≤20, two prominent frequency bands occur, the dominant tone switching back and forth; one band is near screech frequency. This band alone predominates for 2.56≤R≤3.04, and is alone for 3.18≤R≤4.0. Nine stages occur, with 2≤N≤10 and p=0.33 (N+p is the number of cycles in the feedback loop). The jet instability convection speed varies between 0.4UFE and 0.55UFE (UFE is the fully expanded jet velocity), averaging 0.47UFE. Schlieren photographs show that for R<2.36 and 2.9≤ h/δ≤3.4, the jet instability mode and the associated sound fields are symmetric. [Work supported by Texas Advanced Research Program.]