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Space-time aspects of a three-dimensional multi-modulated open cavity flow

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10.1063/1.4811692

### Abstract

Side-band frequencies in an incompressible flow past a rectangular cavity are characterized through their space-time coherent structures. A parametric study over a range of dimensionless cavity length L/θ0 has been carried out in the incompressible regime. It yields the general evolution of self-sustained oscillations, for which primary characteristics match results in the literature. The modulating frequencies associated with side-band frequencies are usually imputed either to the two-dimensional (vortex-edge) interaction at the impingement or to three-dimensional dynamics induced by centrifugal instabilities in the inner-flow. However, secondary order features sometimes depart from commonly accepted scheme. In addition to the salient features of the flow, our observations bring to light another modulation, which may be related to the main recirculation inside the cavity. That modulation even becomes predominant for peculiar configurations. The present work focuses on such a configuration with a cavity length/depth ratio L/D = 1.5 and dimensionless cavity length L/θ0 = 76. Based on time-resolved velocity measurements, the extensive analysis is concerned with the non-linear interactions within the flow. Using laser Doppler velocimetry and time-resolved particle image velocimetry in two planes, this multi-modulated regime is so addressed through both local and global aspects. Time-resolved velocity fields provide space-time coherent data that are analysed using transfer functions, space-time diagrams, and space-extended time-Fourier decomposition.

© 2013 AIP Publishing LLC

Received 10 January 2013
Accepted 28 May 2013
Published online 28 June 2013

Acknowledgments: The authors want to acknowledge Christelle Douay for her contribution to the last PIV measurements. J.B. is grateful to Professor Julio Soria of Monash University for his support and advice. This work has been supported by Direction Generale de l’Armement and Agence Nationale de la Recherche (project ANR-06-BLAN-0363).

Article outline:

I. INTRODUCTION

II. EXPERIMENTS AND DATA PROCESSING

A. Wind tunnel facility

B. LDVmeasurements

C. High-speed PIV measurements in a cross-stream plane

D. Standard PIV measurements in a spanwise plane

E. Optical flow

III. CAVITYFLOW AND CONTEXT

A. Overview and parametric study

B. Case under study: Statistics

IV. LOCAL ANALYSIS: SPECTRAL SIGNATURE

A. Power spectra

B. Time-frequency analysis

V. SPACE-TIME EVOLUTION

A. Shear-layer wave properties

B. Space-time structures and inner-flow interactions

VI. MODAL DECOMPOSITION

A. Shear layer modes

B. Edge interaction *f* _{ b } = *f* _{+} − *f* _{ a } ()

C. Low frequency range and spanwise dynamics

1. Modulating frequency ( 0.12 or 0.08)

2. Broad-band peak (0.014 ⩽ 0.024)

VII. CONCLUSIONS

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/content/aip/journal/pof2/25/6/10.1063/1.4811692

2013-06-28

2014-04-25

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