Influence of non-uniform thermal boundary on flow and heat transfer characteristics in rectangular channel

Abstract

In this paper, the flow behavior and heat transfer characteristic in a rectangular channel are numerically investigated. The non-uniform thermal boundary condition is arranged along the streamwise direction at the bottom of the rectangular channel. Furthermore, based on the flow field parameters obtained with numerical simulation, the dynamic modal decomposition (DMD) is carried out for viscous layer, buffer layer and logarithmic law region respectively. The numerical results show that the heating bands of non-uniform thermal boundary affect the interaction of the velocity streaks along the streamwise direction, which reduces the vorticity of the viscous layer and the fluctuation of the velocity gradient vector. In the terms of entropy analysis, it can be found that the heating bands of non-uniform thermal boundary plays a similar role of "riblets" and blocks the self-sustainment of the turbulent coherent structures. In addition, the results of DMD manifests that the heating bands of non-uniform thermal boundary improve the stability of viscous layer and buffer layer. The development of turbulent boundary layer is delayed by affecting the fluid characteristics in buffer layer. Compared to the channel without non-uniform thermal boundary condition, the maximum drag reduction rate of 8.35% can be achieved in considered cases, while a reduction in heat transfer performance of 2.74% occurs. In addition, the comprehensive performance coefficient increases slightly to 1.0013.