Prof. Bing-Chen Wang

Dept. of Mechanical Engineering, Univ. of Manitoba Winnipeg, Manitoba, Canada

Bio

Dr. Bing-Chen Wang is a Professor in the Department of Mechanical Engineering at the University of Manitoba, Canada. Dr. Wang obtained his B.Sc. (1993) and M.Sc. (1998) degrees from Xi’an Jiaotong University, and Ph.D. degree (2004) from the University of Saskatchewan, Canada.  He joined the University of Manitoba in 2008. Dr. Wang’s current research interests include turbulence theory and modelling, direct numerical simulation, large-eddy simulation, hybrid RANS/LES, convective heat and mass transfer, boundary-layer theory, and environmental flow and dispersion. Currently, Dr. Wang serves as an Associate Editor for Int. J. Heat and Fluid Flow, and serves on the Scientific Advisory Boards for the International Symposium on Turbulence and Shear Flow Phenomena and for the International Symposium on Turbulence, Heat and Mass Transfer.

Title

Direct Numerical Simulation of Turbulent Heat and Fluid Flows in a Channel Roughened with Circular-Arc Ribs

Abstract

Turbulent heat and fluid flows in a cooling channel roughened with circular-arc ribs of different pitch-to-height ratios (P/H=3.0, 5.0 and 7.5) are studied using direct numerical simulations (DNS). The pitch-to-height ratio effects on turbulent convection are studied through analyses of the statistical moments of the velocity and temperature fields. It is interesting to observe that in contrast to the classical channel flow over transverse square bars, the flow separation point in a channel roughened with circular-arc ribs is sensitive to the testing conditions and varies along the rib arc. The flow anisotropy is suppressed as the value of P/H increases due to significant enhancement of the spanwise Reynolds normal stress. It is also interesting to observe that the lifespan of hairpin structures becomes increasingly shortened at the midspan between two adjacent ribs as the pitch-to-height ratio increases. The characteristic spanwise wavelengths of turbulent motions are investigated through a spectral analysis of the transport equation of turbulence kinetic energy (TKE). It is discovered that the turbulent production term is approximately balanced by the interscale transport and dissipation terms associated with small-scale turbulent motions in the inter-rib regions. As the value of P/H increases, the TKE production for sustaining large-scale motions strengthens gradually, whereas the backscatter of TKE from medium- to large-scale turbulence structures becomes increasingly suppressed. The local Nusselt number increases remarkably near the rib center due to the flow impingement on the rib windward side. Furthermore, the thermohydraulic efficiency enhances dramatically in the ribbed channel as the pitch-to-height ratio P/H increases. The quadrant analysis of heated turbulent motions indicates that hot sweep and cold ejection events dominate turbulent heat fluxes near the ribbed bottom wall.