Review—Self-Sustaining Oscillations of Flow Past Cavities

Rockwell, D.; Naudascher, Eduard

doi:10.1115/1.3448624

Cited by 800 publications

(329 citation statements)

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“…1,2 Flows in which self-sustained oscillations occur are (amongst others): jets issuing into a thin cavity, [3][4][5][6][7][8][9] the flow over backward facing steps, 10,11 and flows over cavities. [12][13][14][15] The self-sustained oscillations have a much lower frequency than those produced by shear layer instabilities.…”

Section: Introductionmentioning

confidence: 99%

Effects of electromagnetic forcing on self-sustained jet oscillations

et al. 2014

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The influence of electromagnetic forcing on self-sustained oscillations of a jet issuing from a submerged nozzle into a thin vertical cavity (width W much larger than thickness T) has been studied using particle image velocimetry. A permanent Lorentz force is produced by applying an electrical current across the width of the cavity in conjunction with a magnetic field from three permanent magnets across its thickness. As a working fluid a saline solution is used. The magnetic field is in the north-south-north configuration, such that the Lorentz force can be applied in an up-down-up configuration or in a down-up-down configuration by switching the direction of the electrical current. A critical Stuart number Nc was found. For N < Nc, the jet oscillates with a constant Strouhal number St, independent of the Reynolds number Re. For N > Nc and an oscillation enhancing up-down-up configuration of the Lorentz force, St grows with N as St \documentclass[12pt]{minimal}\begin{document}$\propto \sqrt{\mathrm{N}}$\end{document}∝N. In contrast, for N > Nc and an oscillation suppressing down-up-down configuration of the Lorentz force, all jet oscillations are suppressed.

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Section: Introductionmentioning

confidence: 99%

Effects of electromagnetic forcing on self-sustained jet oscillations

et al. 2014

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“…More details about cavity oscillations in general may be found in review articles (e.g. Rockwell & Naudascher 1978;Blake & Powell 1986); see also the recent work by Howe (1997) for very low Mach number cavity flows, and Crighton (1992) for edge tones.…”

Section: Introductionmentioning

confidence: 99%

“…Note that cavity oscillations have been categorized by Rockwell & Naudascher (1978) into 'fluid-dynamic' oscillations, and 'fluid-resonant' oscillations, where the acoustic resonance of the cavity itself plays an important role, as in a flute or an organ pipe. Both of these classes of oscillations are variations of shear-layer mode, and should not be confused with wake mode.…”

Section: Introductionmentioning

confidence: 99%

On self-sustained oscillations in two-dimensional compressible flow over rectangular cavities

2002

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Numerical simulations are used to investigate the resonant instabilities in twodimensional flow past an open cavity. The compressible Navier-Stokes equations are solved directly (no turbulence model) for cavities with laminar boundary layers upstream. The computational domain is large enough to directly resolve a portion of the radiated acoustic field, which is shown to be in good visual agreement with schlieren photographs from experiments at several different Mach numbers. The results show a transition from a shear-layer mode, primarily for shorter cavities and lower Mach numbers, to a wake mode for longer cavities and higher Mach numbers. The shear-layer mode is characterized well by the acoustic feedback process described by Rossiter (1964), and disturbances in the shear layer compare well with predictions based on linear stability analysis of the Kelvin-Helmholtz mode. The wake mode is characterized instead by a large-scale vortex shedding with Strouhal number independent of Mach number. The wake mode oscillation is similar in many ways to that reported by Gharib & Roshko (1987) for incompressible flow with a laminar upstream boundary layer. Transition to wake mode occurs as the length and/or depth of the cavity becomes large compared to the upstream boundary-layer thickness, or as the Mach and/or Reynolds numbers are raised. Under these conditions, it is shown that the Kelvin-Helmholtz instability grows to sufficient strength that a strong recirculating flow is induced in the cavity. The resulting mean flow is similar to wake profiles that are absolutely unstable, and absolute instability may provide an explanation of the hydrodynamic feedback mechanism that leads to wake mode. Predictive criteria for the onset of shear-layer oscillations (from steady flow) and for the transition to wake mode are developed based on linear theory for amplification rates in the shear layer, and a simple model for the acoustic efficiency of edge scattering. IntroductionOscillations in the flow past an open cavity have been studied for decades, but still there remain many open questions about even the basic physical mechanisms underlying the self-sustained oscillations. Cavity oscillations in compressible flows are typically described as a flow-acoustic resonance phenomenon, and its first detailed description is credited to Rossiter (1964), but it was known earlier as a mechanism for edge tones (e.g. Powell 1953Powell , 1961. In this mechanism, small disturbances in the free shear layer spanning the cavity are amplified via Kelvin-Helmholtz instability. Their interaction with the trailing cavity edge gives rise to an unsteady, irrotational field, † Present address:

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“…Previous studies indicated that the presence of a cavity in a surface bounding flow changes the mean surface pressure distribution and induces high-intensity pressure fluctuations in and near the cavity. [1][2][3][4][5] This may result in structural deflection, strong acoustic radiation, increased drag, or poor optical characteristics for an aerodynamic window. In general, a cavity flow is characterized by a mixture of unsteady flow regimes that include unstable shear layer, pressure waves, and resident vortices oriented in a spanwise direction.…”

Section: Introductionmentioning

confidence: 99%

Geometric Effect on Compressible Rectangular Cavity Flows.

Chung

2002

Trans. Japan Soc. Aero. S Sci.

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Experiments were performed to study the geometric effects on the compressible rectangular cavity flows at Mach 0.33, 0.62, and 0.82. Typical characteristics of mean surface pressure distributions show a slight pressure variation near the front face, a local peak surface pressure ahead of the rear corner, and a low pressure immediately downstream of the cavity. The length-to-width ratio of a cavity has a strong effect on the recompression and downstream expansion near the rear face, and the Mach number effect is minimized. Surface pressure fluctuation distributions show a damping near the leading edge at a higher freestream Mach number, a minor peak near the middle of the cavity floor, an increase toward the cavity rear face, and a peak value immediately downstream of the cavity. The amplitude of the pressure fluctuations ahead of the rear face increases with the length-to-width ratio for transitional-and closed-type cavity flows, and the maximum of peak pressure fluctuations rises rapidly for the transitional cavity flows at higher length-to-width ratio.

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Review—Self-Sustaining Oscillations of Flow Past Cavities

Cited by 800 publications

References 0 publications

Effects of electromagnetic forcing on self-sustained jet oscillations

Effects of electromagnetic forcing on self-sustained jet oscillations

On self-sustained oscillations in two-dimensional compressible flow over rectangular cavities

Geometric Effect on Compressible Rectangular Cavity Flows.

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