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Research Papers: Fundamental Issues and Canonical Flows

# Aero-Acoustic Coupling Inside Large Deep Cavities at Low-Subsonic Speeds

[+] Author and Article Information

Laboratoire de Mécanique et d’Énergetique, Université de Valenciennes, Le Mont Houy, Valenciennes 59300, Franceelhassanmoh@yahoo.fr

Laurent Keirsbulck, Larbi Labraga

Université de Valenciennes, Le Mont Houy, Valenciennes 59300, France

J. Fluids Eng 131(1), 011204 (Dec 02, 2008) (10 pages) doi:10.1115/1.3026725 History: Received July 26, 2007; Revised October 08, 2008; Published December 02, 2008

## Abstract

Aero-acoustic coupling inside a deep cavity is present in many industrial processes. This investigation focuses on the pressure amplitude response, within two deep cavities characterized by their length over depth ratios ($L/H=0.2$ and 0.41), as a function of freestream velocities of a $2×2m2$ wind tunnel. Convection velocity of instabilities was measured along the shear layer, using velocity cross-correlations. Experiments have shown that in deep cavity for low Mach numbers, oscillations of discrete frequencies can be produced. These oscillations appear when the freestream velocity becomes higher than a minimum value. Oscillations start at $L/θ0=10$ and 21 for $L/H=0.2$ and 0.41, respectively. The highest sound pressure level inside a deep cavity is localized at the cavity floor. A quite different behavior of the convection velocity was observed between oscillating and nonoscillating shear-layer modes. The hydrodynamic mode of the cavity shear layer is well predicted by the Rossiter model (1964, “Wind Tunnel Experiments on the Flow Over Rectangular Cavities at Subsonic and Transonic Speeds  ,” Aeronautical Research Council Reports and Memo No. 3438) when measured convection velocity is used and the empirical time delay is neglected. For $L/H=0.2$, only the first Rossiter mode is present. For $L/H=0.41$, both the first and the second modes are detected with the second mode being the strongest.

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## Figures

Figure 1

Three-dimensional view of the cavity

Figure 2

Kulite sensor positions

Figure 3

Pressure spectrum from PS3 (kulite sensor at the leading edge)

Figure 4

Mean streamwise velocity profile upstream of the cavity

Figure 5

Streamwise root-mean-square profile upstream of the cavity

Figure 6

Velocity cross-correlation obtained from two single hot-wires placed in the cavity shear layer

Figure 7

Convection velocity distribution along the cavity shear layer (L/H=0.2)

Figure 8

Convection velocity distribution along the cavity shear layer (L/H=0.41)

Figure 9

Mean convection velocity of structures in the cavity shear layer

Figure 10

Oscillating frequencies for L/H=0.2

Figure 11

Oscillating frequencies for L/H=0.41

Figure 12

Pressure spectra for L/H=0.2

Figure 13

Pressure spectra for L/H=0.41

Figure 14

Spectrogram for L/H=0.2

Figure 15

Spectrogram for L/H=0.41

Figure 16

Maximum pressure level distribution for L/H=0.2

Figure 17

Maximum pressure level distribution for L/H=0.41

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