Large-Eddy Simulation Study of Flow and Heat Transfer in Swirling and Non-Swirling Impinging Jets on a Semi-Cylinder Concave Target

Abstract

Swirling impinging jet (SIJ) is considered as an effective means to achieve uniform cooling at high heat transfer rates, and the complex flow structure and its mechanism of enhancing heat transfer have attracted much attention in recent years. The large eddy simulation (LES) technique is employed to analyze the flow fields of swirling and non-swirling impinging jet emanating from a hole with four spiral and straight grooves, respectively, at a relatively high Reynolds number (Re) of 16,000 and a small jet spacing of H/D = 2 on a concave surface with uniform heat flux. Firstly, this work analyzes two different sub-grid stress models, and LES with the wall-adapting local eddy-viscosity model (WALEM) is established for accurately predicting flow and heat transfer performance of SIJ on a flat surface. The complex flow field structures, spectral characteristics, time-averaged flow characteristics and heat transfer on the target surface for the swirling and non-swirling impinging jets are compared in detail using the established method. The results show that small-scale recirculation vortices near the wall change the nearby flow into an unstable microwave state, resulting in small-scale fluctuation of the local Nusselt number (Nu) of the wall. There is a stable recirculation vortex at the stagnation point of the target surface, and the axial and radial fluctuating speeds are consistent with the fluctuating wall temperature. With the increase in the radial radius away from the stagnation point, the main frequency of the fluctuation of wall temperature coincides with the main frequency of the fluctuation of radial fluctuating velocity at x/D = 0.5. Compared with 0° straight hole, 45° spiral hole has a larger fluctuating speed because of speed deflection, resulting in a larger turbulence intensity and a stronger air transport capacity. The heat transfer intensity of the 45° spiral hole on the target surface is slightly improved within 5–10%.

Heat Transfer Augmentation through Different Jet Impingement Techniques: A State-of-the-Art Review

“…It was observed from the results that heat transfer is enhanced more by well-separated multi-protrusions as compared to V grooves with close spacing. A numerical investigation was conducted by Xu et al [47] for studying the flow fields under jet impingement over a concave surface. The study was performed for swirling and non-swirling jets at a Reynolds number (based on the jet diameter) of 16,000 and jet-target surface spacing H/D = 2.…”

Thermal and dynamic characterization of a multi-jet system with different geometry diffusers

“…In general, the studied swirling impinging jets had a greater spread rate and a more rapid decay in absolute velocity when compared to the non-swirling jet. Xu et al [17] used the LES method of swirling and non-swirling impinging jet from an orifice with four spiral and straight grooves. The local wall-adaptive turbulent viscosity model (WALEM) was chosen to study the relationship between the structure and the heat transfer properties of the square orifice and the spiral orifice for impinging jet cooling.…”

Numerical Investigation and Parameter Sensitivity Analysis on Flow and Heat Transfer Performance of Jet Array Impingement Cooling in a Quasi-Leading-Edge Channel

“…They stated that the shape of the target wall affects the stagnation area size and leads to the difference in flow characteristics of jet impingement cooling. Xu et al [19,20] studied and compared the heat transfer performance of swirling jet impingement cooling and circular hole jet impingement cooling on a semi-cylinder concave target by the large-eddy simulation method. They reported that the wall average Nusselt number of the 45 • angled swirling jet impingement cooling improves by 5% to 10% when compared with circular hole jet impingement cooling.…”