Effect of dimple edge ratio on the thermo-aerodynamic performance in turbulent channel flow

Abstract

In the past few decades, dimples have shown their great capability of enhancing heat transfer along with promising potentials for reducing hydraulic losses and improving the overall thermo-aerodynamic efficiency of turbulent channel flows. In an effort to further optimize the dimple design, this study focuses on the effect of the dimple edge ratio (ER), defined as the ratio between the dimple rounded-edge and base sphere radii, on the channel thermo-aerodynamic performance for ER=0.5, 1, 2, 4, 5, and 10 at two different Reynolds numbers, Reτ ≅180 and 590. For this purpose, the wall-resolved large eddy simulation was used to simulate the flow over the dimples arranged in a staggered form and fitted only on the bottom wall of the channel. Reduction in the required pumping power was observed with increasing the dimple edge ratio up to 4.5% at ER=10 for Reτ ≅180 and around 4% for Reτ ≅590. The thermo-aerodynamic performance of the cases under the study shows an increase in total drag of the dimpled wall for all the cases but accompanied by heat transfer enhancement. The thermo-aerodynamic efficiency was represented in the form of area (Ga) and volume (Gv) goodness factors, where Ga showed almost asymptotic improvement between 1.5% and 2.3% and Gv was observed to have the highest improvement for the benchmark ER value of 0.5 for both Reynolds numbers of 6.8% and 5.8% at Reτ ≅180 and 590, respectively, then reduces with increasing the edge ratio. Overall, all the dimple designs included in this study show improvement in terms of heat transfer performance and thermo-aerodynamic efficiency.