Generation of tones due to flow past a deep cavity: Effect of streamwise length

Abstract

Shear flow past a deep cavity can generate self-sustained oscillations, including locked-on flow tones due to coupling between the inherent instability of the separated shear layer and an acoustic mode of the cavity resonator. This investigation focuses on the pressure amplitude response within a deep cavity, as a function of the streamwise length of the cavity opening; for each length, the pressure amplitude response is characterized over a wide range of inflow velocity.Criteria for locked-on flow tones are assessed; they include: a measure of the strength of lock-on, SoL; and the quality factor Q. All self-excited oscillations are assessed using both of these criteria, in order to interpret dimensionless forms of the fluctuation pressure amplitude.The pressure amplitude response of the cavity involves several successive regimes, due to variations of streamwise length L of the cavity opening. These regimes are defined in relation to L/θ, where θ is the momentum thickness of the inflow boundary layer. Below a minimum value of L/θ, flow tones cannot be generated. Furthermore, these regimes are defined in terms of the possible hydrodynamic modes (stages) of the unsteady shear layer and the acoustic modes of the deep cavity.

An experimental investigation of flow-induced acoustic resonance and flow field in a closed side branch system using a high time-resolved PIV technique

“…The Strouhal number is most important factor as describing the selfinduced vibration. The present range of the Strouhal number agrees with typical St in cavity tones, edge tones (Arthurs and Ziada 2009;Dequand et al 2003;Jungowski et al 1989;Yang et al 2009;Ziada and Bühlmann 1992).…”

An acoustic model of a Helmholtz resonator under a grazing turbulent boundary layer

“…The overlap of both resonance conditions leads to a strong nonlinear interaction of the vortex-sheet with the cavity modes. A qualitative similar behavior of these resonance conditions is also observed for example by Yang's [32] experimental study of deep, open cavities (without a neck). The new Helmholtz resonator model successfully predicts where the occurring physical phenomena are coupled: the Helmholtz base frequency strongly couples with the Kelvin-Helmholtz waves of the neck between 5 m/s and 23 m/s, resulting in a SPL beyond 120dB (s. Fig.…”

Resonant mode characterisation of a cylindrical Helmholtz cavity excited by a shear layer

“…To improve the visibility of the pressure response in figures such as Fig. 10, the receptivity of the cavity to shear layer excitation was quantified using a "strength of lock-on (SoL)" parameter, as suggested by Mendelson 46 and described by Yang et al 7 The parameter chosen was the amplification of the cavity pressure level above the background noise level. Three different positions were explored: D ¼ 99, 39, and 9 mm (L40CC, L40HD, and L40ED, respectively), refer to Fig.…”

“…Tonon et al 6 have studied a series of side branch resonators as a model for flow in a corrugated pipe. Height modes were also studied by Yang et al 7 who specifically analyzed the effect of the stream wise dimension of the cavity and a coaxial side branch configuration was studied by Oshkai and Yan. 8 Panton and Miller 9 conducted seminal work on Helmholtz resonance which has been revisited by Kook deep cylindrical cavity with a rectangular opening.…”