Influence of Cavity Flow Regimes on Turbulence Diffusion Coefficient

Article type: Research Article

Authors: Khan, M. I. | Simons, R. R. | Grass, A. J.

Affiliations: Department of Chemical Engineering, The University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK. E-mail: [email protected] | Civil and Environmental Engineering Department, University College London, Gower Street, London, WC1E 6BT, UK

Abstract: Skimming, wake interference and isolated roughness flow regimes were investigated in the cavity formed between 2-d roughness elements in a laboratory water flume. The flow direction was aligned perpendicular to the roughness elements. Flow visualization and laser Doppler velocimetry were used to confirm the flow pattern and corresponding turbulence characteristics of the flow. Influence of the flow regimes on Reynolds stresses and turbulent diffusion coefficient was investigated at roof level of the cavity. Sweep events towards the wall were significantly affected by the rough bed. A relatively wider cavity demonstrated significant influence on ejection and sweep stresses because of vortex activity at upstream and downstream positions within the cavity. The turbulent diffusion coefficient increased for isolated roughness flow in comparison to skimming flow regime.

Keywords: Turbulence diffusion, Mixing length scale, Bed roughness, Flow pattern

Journal: Journal of Visualization, vol. 9, no. 1, pp. 57-68, 2006