Eddy Resolving Simulations of Shear Layer Instabilities in Open Cavity Flows

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Surface roughness benefits in open cavity flows

In the current study, we report the effect of distributed roughness elements on the flow characteristics within a rectangular cavity using a series of high-fidelity eddy-resolving simulations. A cavity with a length to depth ratio (L/D) of 3 is considered. Simulations are carried out at a Mach number of 0.2 and Reynolds numbers of 7000 and 19300, based on the free-stream velocity and the depth of the cavity. The cavity flows generate undesirable low-frequency pressure fluctuations due to the vortex impingement over the trailing edge of the cavity. We explore the possibility of employing distributed hemispherical roughness elements as a passive flow control strategy towards suppressing these pressure fluctuations. The roughness elements, modeled using the immersed boundary method, are placed upstream of the cavity leading edge and distributed along the span. For a given roughness configuration, we studied the effect of varying Reynolds numbers on the flow features generated by the roughness elements and their interaction with the growth of the separated shear layer using instantaneous and time-averaged flow fields. The roughness elements are shown to effectively reduce the sound pressure level (SPL) up to 7dB for the test cases considered

Surface roughness effects on cavity flows

Effects of three-dimensional (3-D) distributed roughness elements on the flow characteristics within a cavity are investigated using a series of high-fidelity eddy-resolving simulations. The cavity flows generate undesirable low-frequency pressure fluctuations due to the vortex impingement over the trailing edge of the cavity. We explore the possibility of employing distributed hemispherical roughness elements as a passive flow control strategy towards suppressing these pressure fluctuations. A rectangular cavity with a length to depth ratio, L/D, of 3 is considered. Simulations are carried out at a Mach number of 0.2 and Reynolds numbers of 7000 and 19300, based on the free-stream velocity and the depth of the cavity. The effect of sparsely and densely packed roughness elements on the stability of shear layer separating from the cavity are brought out. Pre-transitional fluctuations generated by the roughness elements (a) resulted in transitional/turbulent flow at the cavity leading edge for low/high Reynolds numbers (b) promoted an earlier breakdown of the large-scale coherent structures in the shear layer (c) are beneficial in decreasing the ‘cavity tones’ and the associated sound pressure levels (SPL) by 5-13 dB. Reduction in SPL is observed to be prominent at higher Reynolds numbers and with dense spacing between the roughness elements. At low Reynolds numbers, the benefit obtained by suppressing the ‘cavity tones’ can be eclipsed with an increase in the broadband noise