Heat transfer and flow characteristics in a rectangular channel with small scale vortex generators

Abstract

This article puts forward a novel idea which can be used to control the turbulent coherent structures and make the turbulence more steady by using a “wake blocking wall”. The “wake blocking wall” is induced by small scale vortex generators (miniature cuboids). The flow and heat transfer characteristics in a rectangular channel with a range of miniature cuboid vortex generators (MCVGs) are numerically investigated by large eddy simulation (LES) with ANSYS FLUENT. The height of miniature cuboid is far less than the boundary layer thickness, which means that the cuboids are embed in fully-developed turbulent boundary layer. Furthermore, the spacing between two adjacent cuboids is about one hundred times wall units. The Reynolds number, based on the bulk velocity and channel half-height, is 3745. The influence of the cuboid wake on the turbulent boundary layer is probed. The result indicates that the “wake blocking wall” can alter the coherent structures in turbulent boundary layer, especially the velocity streaky structures. The variation of velocity in viscous sub-layer is mostly suppressed. However, in the logarithmic law region, velocity and temperature gradients are both mostly increased. The overall heat transfer enhancement efficiency is characterized by the synthesis performance coefficient, which includes Nusselt number and skin friction coefficient. The result shows that the wake and vortices induced by cuboids can restrict turbulent movement in spanwise direction, which results in enhancement of the heat transfer performance as well as reduction of the skin-friction in the channel. The Nusselt number and the synthesis performance coefficient increases by 5.17% and 8.15%, respectively.