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ON THE INTERACTION BETWEEN A FORWARD-FACING STEP AND TURBULENT BOUNDARY LAYER

Hannu Eloranta
Energy and Process Engineering Tampere University of Technology P.O. Box 589,33101 Tampere, FINLAND

Penttl Saarenrinne
Energy and Process Engineering Tampere University of Technology P.O. Box 589,33101 Tampere, FINLAND

Tsun-Ya Hsu
Rutgers - The State University of New Jersey Department of Mechanical and Aerospace Engineering 98 Brett Road Piscataway, New Jersey, 08854 - 8085, USA

Timothy Wei
Rutgers - The State University of New Jersey Department of Mechanical and Aerospace Engineering 98 Brett Road Piscataway, New Jersey, 08854 - 8085, USA

Abstract

In this paper the flow around a forward-facing step in a plain channel is studied experimentally using particle image velocimetry and flow visualization. The area of interest lies just upstream of the forward-facing step, particularly in the boundary layer growing on the channel wall opposite to the step. The development of initially turbulent boundary layer under the acceleration generated by the step is assessed by studying both time-mean statistics and instantaneous flow fields. Results show that even though the acceleration parameter K exceeds the critical level of 3.0×10−6, the flow statistics do not reach the characteristics of a quasi-laminar state. However, a remarkable decrease of turbulence activity inside the boundary layer is observed. Besides the mean-flow acceleration, the appearance of other modes of interaction between the step shear layer and the boundary layer is also assessed. Conditional averaging and flow visualization are used to discover if strong instabilities in the shear layer can influence the bottom wall boundary layer. In the region covered by the present measurements, any indication of direct interaction between the step shear layer and the boundary layer flow structures cannot be observed.