Dynamic large eddy simulations of momentum and wall heat transfer in forced convection over wavy surfaces

Abstract

The dynamic large eddy simulations (LES) of flow and heat transfer in a channel with heated wavy bottom walls are performed in the turbulent forced convection regime (Re_b = 11, 200 and 30, 000, Pr = 7). Simulations provided physical insights into the momentum and heat transport over 2D and 3D wavy bottom walls. The numerical validation of the presented dynamic LES showed very good agreement with spectral direct numerical simulations and experimental particle image velocimetry data of both first- and second-order moments for the case with 2D waviness at Re_b = 11, 200. Compared to a plane channel flow, bottom wall waviness generates streamwise and spanwise vortices that enhance heat transfer. The spanwise-oriented coherent structures occur in the separation zone, whereas streamwise-oriented coherent structures are present in the accelerated region of the flow field. For the 2D wavy horizontal wall configuration, the maximum in vertical profiles of the long-term averaged streamwise velocity component is shifted towards the upper flat wall. The instantaneous wall-temperature distribution exhibits a streaky character with high and low temperature regions. In contrast to that, for the 3D wavy wall configuration, reorganisation of the flow and turbulence structures takes place in the immediate proximity of the lower wall. Strong deviations from the standard log-law of the streamwise velocity component are observed for both configurations. At Re_b = 11, 200, the 2D wavy wall configuration was more efficient in transporting heat than the 3D wavy wall – although the difference was relatively small ≈20%.

Keywords:

• large eddy simulation
• forced convection
• wavy wall
• vortical flow structures
• wall heat transfer

Acknowledgements

The numerical work was carried out at TU Delft, Department of Multi-Scale Physics, under the HPC-EUROPA project (RII3-CT-2003-506079), with the support of the European Community Research Infrastructure Action under the FP6 ‘Structuring the European Research Area’Programme. The supercomputing facilities were provided by SARA Amsterdam (www.sara.nl). S.K. acknowledges the ERCOFTAC Leonhard Euler Centre visitor fellowships in 2003, 2004 and 2008 by visits at the Institute of Process Engineering, ETH Zurich.