The aero-acoustic resonance behavior of partially covered slender cavities

Abstract

The present investigation focuses on the aeroacoustic resonance of cavities with a width much larger than their length or depth and partially covered, as often encountered in automotive door gaps. The cavities are under influence of a low Mach number flow with a relatively thick boundary layer. Under certain conditions, these cavities can acoustically resonate with the flow. The upstream and downstream edge of the opening as well as the cover lip overhang location and boundary layer thickness are parametrically varied in an experimental campaign, and the effect of the parameters on the resonance amplitude is investigated. Slender rectangular cavity geometries with an opening length of 8 mm and spanwise width of 500 mm are used. The cavity flow-induced acoustic response is measured with pressure transducers at different spanwise locations inside the cavity. Hot-wire measurements are performed to quantify the boundary layer characteristics. Furthermore, high-speed timeresolved particle image velocimetry is used to capture the instantaneous velocity field around the opening geometries. When the boundary layer thickness is increased, the cavity resonance amplitude diminishes. The cover lip overhang location has a large influence on the resonance response, which can be attributed to changes in the cavity driven flow properties. Rounding of the upstream edge promotes resonance, whereas rounding of the downstream edge can diminish it. A possible explanation of the phenomenon is given on the basis of the PIV observations.

Aeroacoustic Instability Analysis of Helmholtz Resonators Through High-Order Unsteady Reynolds-Averaged Navier–Stokes Simulations

“…The detached shear layer over the cavity can be assumed two-dimensional in case the length-to-width ratio 𝑙/𝑊 is lower than unity. However, the recirculating flow inside the cavity volume has inherently three-dimensional Moreover, for acoustic applications, care needs to be to account for possible influence of the propagating transverse acoustic modes, when the analyzed frequency range is extended beyond the plane wave region [7]. In Fig.…”

“…Previous studies have investigated flow-induced acoustic issues occurring in gas pipe networks [2,3], valves and flow control devices [1], open sunroofs of cars [4][5][6], automotive door gaps [7], aircraft engine liners [8][9][10],…”