Late-stage boundary layer transition mechanisms: A vorticity point of view

Author:

Suryanarayanan Saikishan1ORCID,Goldstein David B.2ORCID,Brown Garry L.3

Affiliation:

1. Department of Mechanical Engineering, The University of Akron 1 , Akron, Ohio 44325, USA

2. Department of Aerospace Engineering and Engineering Mechanics, The University of Texas at Austin 2 , Austin, Texas 78712, USA

3. Department of Mechanical and Aerospace Engineering, Princeton University 3 , Princeton, New Jersey 08544, USA

Abstract

Mechanisms that ultimately lead to the enhanced wall shear stress toward the end of transition to turbulence in a zero-pressure gradient boundary layer are examined for two different transition routes using direct numerical simulations. This paper examines, using a vorticity point of view, late-stage transition mechanisms in roughness induced transition produced by distributed roughness, and a classical transition caused by a large amplitude Tollmien–Schlichting (TS) wave interacting with free stream disturbances adding to the recent insights on discrete roughness induced transition [Suryanarayanan et al., “Roughness induced transition: A vorticity point of view,” Phys. Fluids 31(2), 024101 (2019)]. The Reynolds stress is written in terms of vorticity fluxes, and large negative values of the vorticity flux term associated with the correlation of the spanwise velocity and wall-normal vorticity, w′ωy′¯, are observed in the late-stage transition in all cases. A decrease in wall shear stress is observed when near-wall spanwise motion is suppressed, whereas suppression of spanwise motion far away from the wall does not immediately alter wall shear stress; this observation further supports the finding that w′ωy′¯ is the dominant term that increases wall shear stress during transition. w′ωy′¯ is demonstrated to be correlated with streamwise vorticity near the wall, and this mechanism is illustrated by studying the evolution of a streamwise vortex in a Couette flow.

Funder

Air Force Office of Scientific Research

Publisher

AIP Publishing

Reference36 articles.

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2. Linear stability theory applied to boundary layers;Annu. Rev. Fluid Mech.,1996

3. Linear stability theory and bypass transition in shear flows;Phys. Plasmas,2000

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