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Effect of a mesh on boundary layer transitions induced by free-stream turbulence and an isolated roughness element

Kumar, Phani P and Mandal, AC and Dey, J (2015) Effect of a mesh on boundary layer transitions induced by free-stream turbulence and an isolated roughness element. In: JOURNAL OF FLUID MECHANICS, 772 . pp. 445-477.

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Official URL: http://dx.doi.org/10.1017/jfm.2015.203

Abstract

Streamwise streaks, their lift-up and streak instability are integral to the bypass transition process. An experimental study has been carried out to find the effect of a mesh placed normal to the flow and at different wall-normal locations in the late stages of two transitional flows induced by free-stream turbulence (FST) and an isolated roughness element. The mesh causes an approximately 30% reduction in the free-stream velocity, and mild acceleration, irrespective of its wall-normal location. Interestingly, when located near the wall, the mesh suppresses several transitional events leading to transition delay over a large downstream distance. The transition delay is found to be mainly caused by suppression of the lift-up of the high-shear layer and its distortion, along with modification of the spanwise streaky structure to an orderly one. However, with the mesh well away from the wall, the lifted-up shear layer remains largely unaffected, and the downstream boundary layer velocity profile develops an overshoot which is found to follow a plane mixing layer type profile up to the free stream. Reynolds stresses, and the size and strength of vortices increase in this mixing layer region. This high-intensity disturbance can possibly enhance transition of the accelerated flow far downstream, although a reduction in streamwise turbulence intensity occurs over a short distance downstream of the mesh. However, the shape of the large-scale streamwise structure in the wall-normal plane is found to be more or less the same as that without the mesh.

Item Type: Journal Article
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Additional Information: Copy right for this article belongs to the CAMBRIDGE UNIV PRESS, 32 AVENUE OF THE AMERICAS, NEW YORK, NY 10013-2473 USA
Keywords: boundary layer control; boundary layers; transition to turbulence
Department/Centre: Division of Mechanical Sciences > Aerospace Engineering (Formerly, Aeronautical Engineering)
Date Deposited: 31 Jul 2015 15:55
Last Modified: 31 Jul 2015 15:55
URI: http://eprints.iisc.ernet.in/id/eprint/52001

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