Analysis of Turbulent flow Structures and Heat Transfer with Combined Periodic Oscillation and Swinging Motion of Turbulent Slot Jets

The emergence of highly efficient cooling technologies to establish efficient designs of thermal equipment is in need to satisfy the continuous rise in energy demand. In this respect, jet impingement cooling is considered to be one of the most promising heat transfer augmentation methods. The impinging jets are attributed to high localized heat transfer rates with low-pressure drops. The impinging jets are employed in various industrial and engineering applications in manufacturing and aerospace systems such as gas turbine blade cooling, paper drying, thermal treatment of metals and materials handling, thermal management of high-density electronic equipment, heating and cooling of food products in the food industry, and heating ventilation and air conditioning (HVAC), etc.

The purpose of this study is to investigate the effect of combined periodic oscillation and swinging motion of turbulent jet impinging onto an isothermal surface. For this purpose, the governing equations for continuity, momentum, and energy were solved in the Cartesian framework. The RANS-based two-equation SST k-Omega turbulence model was employed and the algorithm was validated against the case of a turbulent slot jet impinging on an isothermal surface at Re = 20000 for the different jet-to-impingement surface spacing (H/B = 4.0 and 9.2). Further, numerical simulations were performed for different geometric and flow variables viz. Reynolds number [Re = 6000 - 7200], jet-to-impingement surface distance [H = 4.0 and 9.2], and frequencies of periodic oscillation and swinging motion. As the swinging jet oscillates over the isothermal surface, the shear layer between the jet and ambient fluid is observed to oscillate leading to the formation of a vortex street. Also, periodic disruption to the boundary layer was observed instead of a stagnant boundary layer, which may eventually lead to an improved heat transfer. Further, the simulated results comprising fluid flow pattern, temperature distribution, pressure drop, and local and surface averaged Nusselt number along the impingement surface are presented and discussed. The enhancement of surface averaged Nusselt number along the isothermal surface and pressure drop with increasing Reynolds number and reducing jet-to-impingement surface distance are quantified in detail.