Choked‐jet edge‐tone experiments

Abstract

Some experimental results for a choked jet from a 4.8∂:∂ rectangular orifice impinging on a long 8° (w)edge are presented. For nozzle‐edge distance h> three cell lengths, < 15∂ and in the pressure ratio range 2.09 to 3.31, violent edge‐tone oscillations occur that may be above, approximately equal to and merge with, or below the frequency of the simultaneous single screech mode of the free jet. The pressure field (≈evanescent waves) of the growing sinuous jet instability are clearly visible in Schlieren photographs, as is the associated periodic asymmetrical sound field. Preliminary estimates indicate consistency with the proposed feedback formula for the fundamental acoustic wavelength λ [Powell, Acoustica 3, 233–243 (1953)], h′/λ = (N + p) × (Mcon)/(1 + Mcon) with: instability convection Mach number Mcon≈0.5–0.7; nozzle to acoustic source distance h′ ≈ h + 14 × (sinuous instability wavelength); integral number of cycles in the feedback loop N = 4, 5, or 6 with p≈0.4±0.2. Normal hysteretic jumps appear negligible, but other hysteretic effects are suspected. [Partial support from the Texas Advanced Research Program.]