Heat transfer and flow characteristics of a rectangular channel with a small circular cylinder having slit-vent vortex generator

Abstract

The heat transfer and flow characteristics of a rectangular channel with a small scale slit-vent circular cylinder are numerically investigated by Large Eddy Simulation (LES). The small scale circular cylinder is used as vortex generator and located in the boundary layer. The gap ratio G/D (the distance between the lower of the cylinder and the bottom of the channel G to the cylinder diameter D) varies from 0.5 to 6.0. The Reynolds number based on the bulk velocity and half height of the channel is 3745. The influence of gap ratio on cylinder wake and flow structure near the bottom of the channel is probed. Then, the effect of the cylinder wake on the flow and heat transfer features of the channel is revealed. Compared with the result of the rectangular channel without cylinder, it can be found that the interaction between the wake of cylinder and the boundary layer can significantly improve the heat transfer performance of the channel. Compared with the result of the rectangular channel with a reference cylinder whose diameter is the same as the slit-vent cylinder and without slit-vent, it can be found that the impinging jet derived from the slit-vent can further strengthen the interaction between the wake from the lower cylinder and the boundary layer when the gap ratio is less than 2.0. When the gap ratio is more than 2.0, the overall thermal performance of rectangular channel with the slit-vent cylinder is improved, and the constraint of the channel bottom on the wake of the cylinder is gradually weakened. Meantime, the disturbance caused by the wake of the slit-vent cylinder wears off, which leads the synthesis thermal coefficient η lower. The impinging jet has obvious influence on the stability of cylinder wake which related to the features of flow and heat transfer of the channel.