Mechanisms of flow-excited cavity tones at low Mach number

Abstract

Cavity tone spectra have been investigated as a function of wind speed in a low noise wind tunnel, at Mach numbers below 0.2. The cavity, a cylindrical closed pipe with a rectangular slot for a mouth opening, was flush mounted in the side of a flat plate, 30-in. downstream of the leading edge. Both laminar and (tripped) turbulent boundary layer effects were explored. Contributions to tone generation from turbulent boundary layer fluctuations, acoustic background noise, sheartone feedback coupling, and cavity resonant feedback coupling are quantitatively sorted out on the basis of theoretical models. A theory of laminar pipetones, complementing an earlier model of turbulent pipetones, is used as a basis for explaining sheartone/pipetone interaction. An empirical correction curve is introduced to take into account the slowing of wave speed in thick shear layers.

Comparing flyover noise measurements to full-scale nose landing gear wind tunnel experiments for regional aircraft

“…Therefore, the noise levels of both LG systems usually have comparable values [9]. A typical sound signal from a LG system is a combination of broadband noise, mainly caused by the interaction of the LG with the turbulent flow, and tonal noise, generated by noise due to cavities [10,11] and Aeolian tones due to flow separation and vortex shedding [12,13]. The frequency of the tone due to a cavity mainly depends on the cavity geometry itself [10], whereas for Aeolian tones, the tone frequency also depends on the flow velocity.…”

The aero-acoustic resonance behavior of partially covered slender cavities

“…Excitation can be either due to a feedback mechanism of the perturbed shear layer or due to passive excitation by the pressure fluctuations in the turbulent flow (turbulent rumble) (Elder et al 1982). In case of feedback, the shear layer can roll up into discrete vortices impinging on the downstream edge coherently (a Rossiter mode) (Rossiter 1967), or exhibit a flapping shear layer motion.…”

“…If the excitation frequency is close to a resonance frequency, lock-on can occur and the system can resonate. In case of turbulent rumble, the resonance should effectively be independent of velocity (Elder et al 1982).…”

Imaging of acoustically coupled oscillations due to flow past a shallow cavity: effect of cavity length scale

“…Previous studies have provided considerable insight into the generation of flow tones. The variety of configurations addressed in these studies include a jet through a system of orifice plates (Hourigan et al 1990;Stoubos et al 1999), a separated shear layer past a cavity resonator (DeMetz & Farabee, 1977;Elder, 1978;Elder et al, 1982;and Nelson et al 198 1, 1983), and a separated layer past a resonant side branch in the form of a duct or pipe (Pollack, 1980;Bruggeman et al 1989Bruggeman et al , 1991 Kreisels et al 1995 ;Ziada & Buhlmann, 1992;and Ziada & Shine, 1999). Rockwell (1983) and Blake (1986) describe the common elements associated with purely hydrodynamic oscillations.…”

“…(Cremer & king, 1967;Bruggernan, 1987;Ziada, 1994;Kriesels el al. 1995;Hourigan et al 1990;Nelson et al 1981;and Huang & Weaver, 1991) and pointwise measurements of flow characteristics (Elder, 1978;Elder et al 1982;Schachenmann & Rockwell, 1980;Rockwell & Schachenmann, 1982a, 1982bNelson et al 1981;and Coccola, 2000).…”