Title: Backward-facing step flows for various expansion ratios at low and moderate Reynolds numbers
Authors: Biswas, Gautam
Breuer, Michael  
Durst, Franz
Language: eng
Issue Date: May-2004
Document Type: Article
Journal / Series / Working Paper (HSU): Journal of Fluids Engineering, Transactions of the ASME
Volume: 126
Issue: 3
Page Start: 362
Page End: 374
This paper is concerned with the behavior of flows over a backward-facing step geometry for various expansion ratios H/h =1.9423, 2.5 and 3.0. A literature survey was carried out and it was found that the flow shows a strong two-dimensional behavior, on the plane of symmetry, for Reynolds numbers Re D=ρUb,D/μ below approximately 400 (Ub, =bulk velocity and D=hydraulic diameter). In this Reynolds number range, two-dimensional predictions were carried out to provide information on the general integral properties of backward-facing step flows, on mean velocity distributions and streamlines. Information on characteristic flow patterns is provided for a wide Reynolds number range, 10-4≤Re D≤800. In the limiting case of ReD→0, a sequence of Moffatt eddies of decreasing size and intensity is verified to exist in the concave corner also at ReD=1. The irreversible pressure losses are determined for various Reynolds numbers as a function of the expansion ratio. The two-dimensional simulations are known to underpredict the primary reattachment length for Reynolds numbers beyond which the actual flow is observed to be three-dimensional. The spatial evolution of jet-like flows in both the streamwise and the spanwise direction and transition to three-dimensionality were studied at a Reynolds number ReD =648. This three-dimensional analysis with the same geometry and flow conditions as reported by Armaly et al. (1983) reveals the formation of wall jets at the side wall within the separating shear layer. The wall jets formed by the spanwise component of the velocity move towards the symmetry plane of the channel. A self-similar wall-jet profile emerges at different spanwise locations starting with the vicinity of the side wall. These results complement information on backward-facing step flows that is available in the literature.
Organization Units (connected with the publication): Universität Erlangen-Nürnberg
ISSN: 00982202
Publisher DOI: 10.1115/1.1760532
Appears in Collections:Publications of the HSU Researchers (before HSU)

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