The thermo-aerodynamic performance of turbulent channel flow over dimples of different sizes

Abstract

Dimples were introduced as a passive method for heat transfer enhancement and a potential drag reduction tool. However, besides the flow parameters, dimples have several design parameters that control their thermal and dynamic performance. To find the optimal design to improve dimples' performance, each parameter's effect has to be investigated. In this study, we show the effect of different dimples' sizes and flow Reynolds numbers on heat transfer and drag performance of a turbulent channel flow. Wall-resolved Large Eddy Simulation has been used to simulate the flow over the dimples fitted only on the bottom wall of the channel. The flow is simulated over three different sizes with dimensionless diameters D+=2.5, 4π/3, and 5 along with three different friction Reynolds numbers Reτ ≅180, 395, and 590. The dimples are arranged in a staggered form with smooth rounded edges of radius equal to half dimple's base radius along with constant maximum allowable coverage ratio and depth-to-diameter ratio of 5%. The thermo-aerodynamic performance of the cases under study shows an increase in drag for all the cases but accompanied by heat transfer enhancement. The thermo-aerodynamic efficiency, represented in area and volume goodness factors, shows an increase up to around 2%, and 6.8% compared to the flat channel, respectively, with the area goodness factor to be affected by the dimple size more than Reynolds number.