Flow and heat transfer in straight cooling passages with inclined ribs on opposite walls: an experimental and computational study

This paper discusses the results of a combined experimental and numerical study of flow and heat transfer in a straight duct, with ribs of square cross section along two opposite walls, in a staggered arrangement and at an angle of 45degrees to the main flow direction. The mean and fluctuating fluid motions are measured using laser Doppler anemometry and the local Nusselt number with the steady-state liquid crystal technique. Flow computations have been produced using a three-dimensional, non-orthogonal flow solver, with two 2-layer models of turbulence (an effective-viscosity model and a second-moment closure), in which across the near-wall regions the dissipation rate of turbulence is obtained from the wall distance. The flow and thermal developments are found to be dominated by the rib-induced secondary motion, which leads to strong spanwise variations in the mean flow and the local Nusselt number and in a uniform distribution of turbulence intensities across the duct. Both 2-layer turbulence models produce satisfactory predictions of the mean and turbulence motions. Somewhat surprisingly, considering the findings of earlier studies for ducts with ribs normal to the flow, both 2-layer models also returned similar Nusselt number distributions. The main features of the measured variation of the local Nusselt number are reproduced, but the actual Nusselt number levels are over-predicted, especially by the 2-layer k-epsilon model. (C) 2002 Elsevier Science Inc. All rights reserved.