Re-laminarization and re-transition of a turbulent boundary layer from a vorticity point of view

Brown, GL and Patwardhan, SS and Ramesh, ON (2017) Re-laminarization and re-transition of a turbulent boundary layer from a vorticity point of view. In: 10th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2017, 6 July 2017 - 9 July 2017, chicago.

PDF TSFP_2-2017.pdf - Published Version Restricted to Registered users only Download (4MB) | Request a copy

Abstract

The presentation at TSFP 9 by Brown, Lee and Moser (2015) on the near wall transfer of viscous stress to Reynolds stress, based on a vorticity transport perspective, was motivated by the connection between the transport of vorticity and the Reynolds stress, i.e. (for plane, parallel turbulent flow) to which Taylor (1915) first drew attention. That work has now been expanded to include Couette flow and is being submitted for publication (BLM (2017)). We consider here the role played by these vorticity transport terms in an understanding of the mechanics of a highly accelerating, re-laminarizing, turbulent boundary layer. An initial, zero pressure gradient, turbulent boundary layer is accelerated by a very favorable pressure gradient, which provides an increase by a factor of three in free stream velocity. It is followed by a relaxation towards zero pressure gradient at this much higher free stream velocity. A recent experimental and numerical investigation (Patwardhan (2015), Patwardhan and Ramesh (2017)) shows a dramatic fall in local skin friction coefficient and, particularly, a local fall in the actual wall friction due to this acceleration. Since an acceleration and fall in static pressure is a source of spanwise vorticity at the wall this decrease in wall vorticity demands a mechanistic explanation. A 're-laminarization' of the near wall flow, as the flow accelerates, is found, which is then followed by a re-transition to turbulence in the subsequent, approximately zero pressure gradient, flow. This relaminarizing flow attracted early experimental and theoretical attention by Sreenivasan (1972), and Narasimha and Sreenivasan (1973, 1979)) who provided a mechanistic description, largely based on momentum considerations. They developed a two layer model with the idea of a 'laminar sub boundary layer' near the wall and a 'rapid distortion' model for the outer flow, but it was not possible at that time to measure the components of vorticity near the wall. DNS computions now offer detailed and complementary insights. In particular these computations provide results for the vorticity field and for the vorticity transport terms in the above equation.

Item Type:	Conference Paper
Publication:	10th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2017
Publisher:	International Symposium on Turbulence and Shear Flow Phenomena, TSFP10
Additional Information:	The copyright for this article belongs to International Symposium on Turbulence and Shear Flow Phenomena, TSFP10
Keywords:	Boundary layer flow; Boundary layers; Buoyancy; Friction; Laminar boundary layer; Parallel flow; Pressure gradient; Reynolds number; Shear flow; Turbulence; Turbulent flow; Vorticity; Wall flow, Favorable pressure gradients; Free-stream velocity; Local skin-friction coefficient; Momentum considerations; Numerical investigations; Turbulent boundary layers; Vorticity transports; Zero pressure gradient, Atmospheric thermodynamics
Department/Centre:	Division of Mechanical Sciences > Aerospace Engineering(Formerly Aeronautical Engineering)
Date Deposited:	27 Jul 2022 10:12
Last Modified:	27 Jul 2022 10:12
URI:	https://eprints.iisc.ac.in/id/eprint/74732

Actions (login required)

View Item