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research-article

Experimental Investigation of Boundary Layer Relaminarization in Accelerated Flow

[+] Author and Article Information
Pascal Bader

Graduate Research Assistant, Institute for Thermal Turbomachinery and Machine Dynamics, Graz University of Technology, Graz, 8010, Austria
pascal.bader@tugraz.at

Manuel Pschernig

Undergraduate Research Assistant, Institute for Thermal Turbomachinery and Machine Dynamics, Graz University of Technology, Graz, 8010, Austria
pschernig.manuel@gmx.net

Wolfgang Sanz

Professor, Head of Department, Institute for Thermal Turbomachinery and Machine Dynamics, Graz University of Technology, Graz, 8010, Austria
wolfgang.sanz@tugraz.at

Jakob Woisetschlaeger

Professor, Head of Department, Institute for Thermal Turbomachinery and Machine Dynamics, Graz University of Technology, Graz, 8010, Austria
jakob.woisetschlaeger@tugraz.at

Franz Heitmeir

Professor, Head of Institute, Institute for Thermal Turbomachinery and Machine Dynamics, Graz University of Technology, Graz, 8010, Austria
franz.heitmeir@tugraz.at

Walter Meile

Professor, Head of Department, Institute of Fluid Mechanics and Heat Transfer, Graz University of Technology, Graz, 8010, Austria
walter.meile@tugraz.at

Günter Brenn

Professor, Head of Institute, Institute of Fluid Mechanics and Heat Transfer, Graz University of Technology, Graz, 8010, Austria
guenter.brenn@tugraz.at

1Corresponding author.

ASME doi:10.1115/1.4039257 History: Received June 27, 2017; Revised December 11, 2017

Abstract

Flow in turbomachines is generally highly turbulent. Nonetheless, boundary layers may exhibit laminar-to- turbulent transition, and relaminarization of the turbulent flow may also occur. The state of flow of the boundary layer is important since it influences transport phenomena like skin friction and heat transfer. In the present paper, relaminarization in accelerated flat-plate boundary-layer flows is experimentally investigated, measuring flow velocities with laser-Doppler anemometry. Besides the mean values, statistical properties of the velocity fluctuations are discussed in order to understand the processes in relaminarization. It is shown that strong acceleration leads to a suppression of turbulence production. The velocity fluctuations in the accelerated boundary layer flow "freeze", while the mean velocity increases, thus reducing the turbulence intensity. This leads to a laminar-like velocity profile close to the wall, resulting in a decrease of the local skin friction coefficient. Downstream from the section with enforced relaminarization, a rapid re-transition to turbulent flow is observed. The findings of this work also describe the mechanism of re-transition.

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