Date of Award

8-2021

Document Type

Dissertation - Open Access

Degree Name

Doctor of Philosophy in Aerospace Engineering

Department

Aerospace Engineering

Committee Chair

Dr. Mark Ricklick

First Committee Member

Dr. Magdy S. Attia

Second Committee Member

Dr. Sandra Boetcher

Third Committee Member

Dr. Reda Mankbadi

Abstract

Jet impingement cooling is a widely used cooling method due to the high heat transfer rates associated with it. Research for improving heat transfer rates for this cooling is still being carried out due to its broad application in various fields like gas turbine blade cooling, electronic component cooling, and paper drying. The unsteady jet oscillation effectively enhances the stagnation region and the time-averaged heat transfer rates. It is shown that a novel passive jet oscillation technique can be achieved using the vortices periodically shed from a cylinder placed upstream in a channel with an initial crossflow. Preliminary CFD results prove the hypothesis of jet oscillation induced by the cylinder vortices and that the lateral jet oscillation is an efficient method for uniform distribution of heat transfer. The statistical analysis concluded jet oscillation is most sensitive to cylinder vortex strength. A frequency spectral analysis is performed to classify oscillating and non-oscillating cases. Finally, unsteady numerical and experimental research is carried out to determine the effect of cylinder-jet distance, cylinder diameter, and velocity ratio on jet oscillation and heat transfer rate. The range of cylinder-jet distance and velocity ratio tested are S/d = 2 – 4 and VR = 4 – 12, respectively. The flow interaction mechanism leading the jet oscillation is analyzed using TKE, vorticity, and velocity contours in time. The flow feature analysis concluded the cylinder wakes deformed the jet core inducing lateral and angular oscillations. The heat transfer results showed the Nusselt number is proportional to the velocity ratio for oscillating jet cases. The non-oscillating jet enhances the heat transfer rate by 94% in the wall jet region due to crossflow interaction. And the optimum oscillating jet case improved the stagnation region Nusselt number by 19%.

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