Experimental and Theoretical Investigations of Edge Tones in High Speed Jets

Abstract

Experimental and theoretical investigations of the high speed jets impinge on a wedgeshaped edge have been conducted. Sonic circular and square jets of the same hydraulic diameter are examined in the present study. Edge-tones produced due to a wedgeshaped edge having different angles, specifically, 10 o , 20 o , 60 o and 180 o , have been investigated. Experiments reveal that several instability modes exist simultaneously in the microphone-captured acoustic signal. The minimum breadth is defined as the minimum distance of the edge from the nozzle exist for the first tone to be generated. Experiments showed that at small edge angle, the minimum breadth is approximately half of its equivalent two-dimension case. Semi-empirical frequency formula for the dominant tone is proposed based on the present experimental data for small edge angles. The theoretical results based on the vortex-sheet model proposed by Tam and Ahuja (1) showed that both helical and axisymmetric stability modes exist during jet impingement. The dominant tone usually has helical stability mode which is the well known edge-tone. Other tones are known as impinging-tones in the literatures and have axisymmetric stability modes. Finally, it has been shown that the experimentally obtained mean Strouhal numbers for helical and axisymmetric modes show good agreement with the Strouhal number of the least dispersive wave of the same mode calculated at various Mach numbers.

A Theoretical and Experimental Investigation on Ejector Acoustics and Ejector Silencer Design

“…Reference [62] explains that while these will affect the flow, they are secondary factors which have a much smaller effect than the variables in formula 3.7. To further elaborate on this, reference [67] finds that the wedge angle has little impact under 40 • and reference [63] experiences tones for all wedge angles investigated (10 • , 20 • , 60 • and 180 • ).…”

“…As the jet velocity or the nozzle to wedge distance changes the frequency of the tone changes gradually until the oscillation abruptly changes modes in a discrete fashion. Edge tone studies typically make use of a planar nozzle (rectangular cross section with a high aspect ratio) [63] Most studies use low speed flows (low Reynolds numbers)…”