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Research Papers

# Mechanisms of Self-Sustained Oscillations Induced by a Flow Over a Cavity

[+] Author and Article Information
Michel Massenzio1

Université de Lyon, Lyon F-69003, France; Université Lyon 1, UMRT 9406, IUT B GMP 17, rue de France, 69627 Villeurbanne Cedex, Francemichel.massenzio@iutb.univ-lyon1.fr

Alain Blaise

ISTIL, UFR Mécanique, Université Lyon 1, 43 Bd du 11 Novembre 1918, 69622 Villeurbanne Cedex, France

Claude Lesueur

ISAT, 49 rue Mademoiselle Bourgeois, 58027 Nevers Cedex, France

1

Corresponding author.

J. Vib. Acoust 130(5), 051001 (Aug 12, 2008) (8 pages) doi:10.1115/1.2948367 History: Received March 08, 2006; Revised January 30, 2008; Published August 12, 2008

## Abstract

This paper discusses the phenomena of flow-acoustic coupling between an unstable shear layer across a slot covering a cavity, thereby forming a Helmholtz resonator. The flow was caused by a turbulent boundary layer flowing over the slot. The physical phenomena implicated were responsible for the generation of high-amplitude sound level that occurred at the resonant frequencies of the system. It concerns a wide variety of applications, especially in the transport industry. Cavity oscillations have been studied steadily for some $50years$ and there is by now a vast and conflicting literature on the measured tonal frequencies, the physical explanations, and the predictive models for them. A theory was presented to predict the onset of the instability. It was based on the identification of the main parameters that played a role in the shear layer. Particularly it was suggested to use the frequency dependent phase velocity instead of the flow velocity. The theory was then confronted with results obtained from an experimental study carried out in a wind tunnel on several models. This validation underlined the sturdiness and the efficiency of the model, which made it useful for engineering applications.

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## Figures

Figure 1

The elementary problem: the Helmholtz resonator and the flow (left) and the feedback mechanism (right)

Figure 2

Nondimensional phase velocity versus nondimensional frequency (from Ref. 40)

Figure 3

Sound pressure level in the cavity NC1−U∞=28m∕s

Figure 4

NC1 model: Relationship between flow velocity, discrete frequency, and SPL in the cavity (CT: coupled tone and ST: shear tone)

Figure 5

SPD of the x and z components of the instantaneous velocity, measured at the interface of NC1 model, 3ℓ∕4 from the leading edge (U∞=29m∕s)

Figure 6

Mean square value of x and z components of instantaneous velocity near the interface, NC1 model

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