Slip effects on turbulent heat transport over post and ridge structured superhydrophobic surfaces

Forced convection and turbulent scalar transport over a structured superhydrophobic walls composed of periodic arrays of square posts and ridges textures are numerically investigated in a periodic channel. The flow physics and thermal transport within the fluid are studied using Direct numerical simulation (DNS), assuming the plastrons are flat. Slip velocities, Nusselt number, turbulent Prandtl number and turbulent heat fluxes are determined for both square posts and streamwise ridge shaped feature geometry configurations at a friction Reynolds number of Re-tau = 180. This article provides an insight that superhydrophobic surfaces enhance turbulent heat fluxes and thermal fluctuations in the laminar-sublayer region. With increasing feature wavelength, the turbulent heat fluxes in the buffer layer and outer layer drop for both square posts and streamwise ridges. When compared with a smooth no-slip channel, the diffusion term in the budget of thermal fluxes pointed to the role of organized lateral flow motions in enhancing wall-normal heat-flux, and a reduction in large scale transport of streamwise heat fluxes by near-wall coherent structures. (C) 2018 Elsevier Ltd. All rights reserved.