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Fundamental Issues and Canonical Flows

Control of Cavity Flow Oscillations by High Frequency Forcing

[+] Author and Article Information
M. A. Martinez, G. M. Di Cicca, M. Iovieno, M. Onorato

 DIASP, Politecnico di Torino,Corso Duca degli Abruzzi, 24, 10129 Torino, Italy

J. Fluids Eng 134(5), 051201 (May 07, 2012) (11 pages) doi:10.1115/1.4006468 History: Received July 29, 2011; Revised March 22, 2012; Published May 03, 2012; Online May 07, 2012

Time resolved two-dimensional particle image velocimetry (2DPIV) experiments have been conducted to contribute to the understanding of the physics governing the suppression mechanism of cavity flow self-sustained oscillations by means of high frequency excitation of the cavity shear layer. High frequency excitation was introduced by the spanwise coherent vortex shedding in the wake of a cylindrical rod positioned just upstream the cavity entrance, at the edge of the incoming boundary layer. The effectiveness of this suppression was demonstrated for a cavity having the length-to-depth ratio equal to three, in incompressible flow. The spatial and time resolved PIV measurements of the whole flow field in the plane normal to the cavity floor, linear stability analysis of the measured shear layer mean velocity profiles, and preliminary PIV measurements in a plane parallel to the cavity allowed us to offer a better insight into the involved physical mechanisms in suppressing cavity self-sustained oscillations.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Experimental setup

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Figure 2

Mean velocity profiles at the cavity leading edge for the baseline and the controlled flows

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Figure 3

Normalized streamwise (u/ue ) and bottom wall normal (v/ue ) mean velocity profiles at different distances from the leading edge. Each velocity profile is shifted by 1 with respect to the previous one. Plain symbols: baseline flow. Empty symbols: controlled flow.

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Figure 4

Final position yf of the streamlines at x/H = 2.9 as a function of the initial position yi at x/H = 0.05

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Figure 5

Normalized standard deviation of the streamwise fluctuating velocity: (a) baseline flow u′BF /ue ; (b) controlled flow u′CF /ue . Normalized standard deviation of the bottom wall normal fluctuating velocity: (c) baseline flow v′BF /ue ; (d) controlled flow v′CF /ue . (e) → (b)–(a); (f) →(d)–(c). Dashed lines indicate negative values.

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Figure 6

Normalized mean vorticity: (a) baseline flow ωBF H/ue ; (b) controlled flow ωCF H/ue . Normalized vorticity standard deviation: (c) baseline flow ω′BF H/ue ; (d) controlled flow ω′CF H/ue . (e) → (b)–(a); (f) → (d)–(c). Dashed lines indicate negative values.

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Figure 7

Visualization of the instantaneous swirling strength. (a) Basic flow and (b) controlled flow. Dark gray: clockwise vortices (negative). Light gray: counterclockwise vortices (positive). More intense gray levels correspond to stronger vortices.

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Figure 8

Normalized power spectral density P(adim)  = Pv /(ue H) of the bottom wall normal component of the velocity along the cavity mouth, at different distances from the leading edge. Black line: baseline flow. Gray line: controlled flow.

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Figure 9

Dimensionless spatial amplification factor as function of the Strouhal number. Plain symbols: baseline flow. Empty symbols: controlled flow.

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Figure 10

Instantaneous cavity drag coefficient per unit spanwise length in function of time (seconds)

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Figure 11

Conditional averaged streamlines

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Figure 12

Instantaneously detected vortices superimposed to the velocity field for the baseline flow

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Figure 13

Spanwise autocorrelation function of the streamwise component of the velocity at y/H = 0.05 and at different distances from the cavity leading edge. Plain symbols: baseline flow. Empty symbols: controlled flow. (a) x/H = 0.4; (b) x/H = 1.1; and (c) x/H = 2.9.

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