Flow characteristics and thermal fields in fan-coupled jet impingement

Abstract

Numerical methods are used to analyze the flow properties and thermal fields of a fan-coupled jet impingement. The shear stress transport(SST) k−ω model has been utilized in the numerical simulation conducted in ANSYS CFX. Initially, the study focuses on flow structures that are driven by pressure gradients. Due to the presence of the pressure gradient, there is a tip leakage vortex moving through the tip gap. In the vicinity of the hub, the boundary layer rolls up to form a passage vortex close to the blade. The presence of these secondary flow structures affects the features of the cooling flow provided by the axial fan. Velocity deficit and high turbulence exist in the regions as a result of the secondary flow structures. Furthermore, to demonstrate how the 3D structures affect the performance of the jet impingement, two comparison cases, named LF-Q and LF-curve, are introduced with uniform incoming flow. In the comparison cases, the axial fan is abstracted as a solid body with pressure rise and flow rate. Compared to the counterparts with uniform incoming flow, the fan-coupled jet shows a greater re-circulation and a narrower main jet as a result of the velocity deficit exiting near the hub. In terms of thermal performance, the fan-coupled jet outperforms a uniform impinging jet with the same flow rate by 1.18 times in total heat transfer. The velocity deficit and larger re-circulation have reduced the heat transport in the central target, while the mainstream with high velocity and strong turbulence has enhanced the heat transfer in the outer region. The fan-coupled jet impingement with high velocity in the narrower jet also shows improved local heat transfer, with a peak Nusselt number (Nu) approximately 1.37 times larger than that of the uniform case with the same flow rate.