Effects of Shear-Layer Characteristic on the Feedback-loop Mechanism in Supersonic Open Cavity Flows

2011 ◽  
Author(s):  
Weipeng Li ◽  
Taku Nonomura ◽  
Kozo Fujii
Keyword(s):  
Shear Layer ◽  
Feedback Loop ◽  
Open Cavity ◽  
Cavity Flows ◽  
Layer Characteristic

On the modulating effect of three-dimensional instabilities in open cavity flows

2014 ◽  
Vol 759 ◽  
pp. 546-578 ◽  
Author(s):  
J. Basley ◽  
L. R. Pastur ◽  
F. Lusseyran ◽  
J. Soria ◽  
N. Delprat
Keyword(s):  
Shear Layer ◽  
Travelling Waves ◽  
Broad Band ◽  
Three Dimensional ◽  
High Energy ◽  
Open Cavity ◽  
Coupling Mechanism ◽  
Cavity Flows ◽  
Low Frequencies ◽  
Sustained Oscillations

AbstractOpen cavity flows are known to select and enhance locked-on modes or tones. High-energy self-sustained oscillations arise within the shear layer, impinging onto the trailing edge of the cavity. These self-sustained oscillations are subject to amplitude modulations (AMs) at multiple low frequencies. However, only a few studies have addressed the identification of the lowest modulating frequencies. The present work brings to light salient AMs of the shear layer waves and identifies their source as three-dimensional dynamics existing inside the cavity. Indeed, the recirculating inner flow gives rise to centrifugal instabilities, which entail broad-band frequencies down two orders of magnitude lower than those of the self-sustained oscillations. Using time-resolved PIV (TRPIV) in two planes, the nonlinearly saturated dynamics is analysed in both space and time by means of proper orthogonal decomposition, global Fourier decomposition and Hilbert–Huang transforms. The inner flow can be decomposed as three-dimensional waves carried by the main recirculation. Bicoherence distributions are computed to highlight the nonlinear interactions between these spanwise-travelling waves inside the cavity and the locked-on modes. The modulated envelope of the shear layer oscillations is extracted and investigated with regards to the inner-flow dynamics. Strong cross-correlations, in time rather than in space, reveal a global coupling mechanism, possibly related to the beating of the spanwise-travelling waves.

Characteristics of Oscillations in Supersonic Open Cavity Flows

2012 ◽  
Vol 90 (1) ◽  
pp. 121-142 ◽  
Author(s):  
Hongbo Wang ◽  
Mingbo Sun ◽  
Ning Qin ◽  
Haiyan Wu ◽  
Zhenguo Wang
Keyword(s):  
Open Cavity ◽  
Cavity Flows

Experimental study of physical mechanisms in the control of supersonic impinging jets using microjets

2008 ◽  
Vol 613 ◽  
pp. 55-83 ◽  
Author(s):  
FARRUKH S. ALVI ◽  
HUADONG LOU ◽  
CHIANG SHIH ◽  
RAJAN KUMAR
Keyword(s):  
Shear Layer ◽  
Nozzle Exit ◽  
Feedback Loop ◽  
Large Scale ◽  
Impinging Jet ◽  
Impinging Jets ◽  
Operating Conditions ◽  
Jet Flows ◽  
Streamwise Vorticity ◽  
Control Approach

Supersonic impinging jet(s) inherently produce a highly unsteady flow field. The occurrence of such flows leads to many adverse effects for short take-off and vertical landing (STOVL) aircraft such as: a significant increase in the noise level, very high unsteady loads on nearby structures and an appreciable loss in lift during hover. In prior studies, we have demonstrated that arrays of microjets, appropriately placed near the nozzle exit, effectively disrupt the feedback loop inherent in impinging jet flows. In these studies, the effectiveness of the control was found to be strongly dependent on a number of geometric and flow parameters, such as the impingement plane distance, microjet orientation and jet operating conditions. In this paper, the effects of some of these parameters that appear to determine control efficiency are examined and some of the fundamental mechanisms behind this control approach are explored. Through comprehensive two- and three-component velocity (and vorticity) field measurements it has been clearly demonstrated that the activation of microjets leads to a local thickening of the jet shear layer, near the nozzle exit, making it more stable and less receptive to disturbances. Furthermore, microjets generate strong streamwise vorticity in the form of well-organized, counter-rotating vortex pairs. This increase in streamwise vorticity is concomitant with a reduction in the azimuthal vorticity of the primary jet. Based on these results and a simplified analysis of vorticity transport, it is suggested that the generation of these streamwise vortices is mainly a result of the redirection of the azimuthal vorticity by vorticity tilting and stretching mechanisms. The emergence of these longitudinal structures weakens the large-scale axisymmetric structures in the jet shear layer while introducing substantial three-dimensionality into the flow. Together, these factors lead to the attenuation of the feedback loop and a significant reduction of flow unsteadiness.

Subsonic Flow Over Open Cavities: Part 1 — Analytical Models and Numerical Investigations

2016 ◽  
Author(s):  
Weidong Shao ◽  
Jun Li
Keyword(s):  
Boundary Layer ◽  
Mach Number ◽  
Shear Layer ◽  
Layer Thickness ◽  
Boundary Layer Thickness ◽  
Feedback Loop ◽  
Subsonic Flow ◽  
Free Stream ◽  
Open Cavities ◽  
Free Stream Mach Number

The aeroacoustical oscillation and acoustic field generated by subsonic flow grazing over open cavities has been investigated analytically and numerically. The tone generation mechanism is elucidated with an analytical model based on the coupling between shear layer instabilities and acoustic feedback loop. The near field turbulent flow is obtained using two-dimensional Large Eddy Simulation (LES). A special mesh is used to absorb propagating disturbances and prevent spurious numerical reflections. Comparisons with available experimental data demonstrate good agreement in both the frequency and amplitude of the aeroacoustical oscillation. The physical phenomenon of the noise generated by the feedback loop is discussed. The correlation analysis of primitive variables is also made to clarify the characteristics of wave propagation in space and time. The effects of free-stream Mach number and boundary layer thickness on pressure fluctuations within the cavity and the nature of the noise radiated to the far field are examined in detail. As free-stream Mach number increases velocity fluctuations and mass flux into the cavity increase, but the resonant Strouhal numbers slightly decrease. Both the resonant Strouhal numbers and sound pressure levels decrease with the increase of boundary layer thickness. Results indicate that the instability of the shear layer dominates both the frequency and amplitude of the aeroacoustical oscillation.

Experimental and computational study of laminar cavity flows at hypersonic speeds

2001 ◽  
Vol 427 ◽  
pp. 329-358 ◽  
Author(s):  
A. P. JACKSON ◽  
R. HILLIER ◽  
S. SOLTANI
Keyword(s):  
Shear Layer ◽  
Cavity Length ◽  
Computational Study ◽  
Vortex Formation ◽  
Three Dimensional ◽  
Cavity Flows ◽  
Free Shear Layer ◽  
Closed Cavity ◽  
Turbulent Transition ◽  
Hypersonic Speeds

This paper presents a combined experimental/computational study of a surface cavity in a low Reynolds number Mach 9 flow. The geometry is based on a body of revolution, which produces highly two-dimensional time-averaged flow for all experimental test cases. A range of cavity length-to-depth ratios, up to a maximum of 8, is investigated. These correspond to ‘closed’ cavity flows, with the free shear layer bridging the entire cavity. For most cases the free shear layer is laminar. However, there is evidence of three-dimensional unsteadiness which is believed to be the consequence of Taylor–Görtler-type vortex formation. The effect of this is first detected on the cavity floor but progressively spreads as the cavity length is increased. For the longest cavities the flow is also influenced by the early stages of laminar–turbulent transition in the free shear layer.

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