Date of Award

Spring 5-2021

Access Type

Dissertation - Open Access

Degree Name

Doctor of Philosophy in Aerospace Engineering

Department

Aerospace Engineering

Committee Chair

Mark Ricklick

First Committee Member

J. Gordon Leishman

Second Committee Member

William Engblom

Third Committee Member

Sandra K.S. Boetcher

Abstract

Array of circular cylindrical pins or tubes are one of the most widely used type of convection cooling systems, profoundly used in the internal cooling of gas turbine blades. They promote heat transfer due to flow acceleration, secondary flows and wake shedding, at the expense of large pressure loss and unsteadiness in the flow. The need to reduce pressure loss and maintain the heat transfer rates are a much needed requirement for a variety of industries to improve the cooling efficiency. One such prominent line of research is conducted on optimizing the design of the circular cylindrical pins to increase their cooling performance. Bio-mimicked harbor seal whisker have been studied from an aerodynamic standpoint, due to their ability to reduce drag and flow unsteadiness. While applying this mimicked geometry in thermal management research, it was found that they lead to reduction in cooling system pumping power requirements, with the potential to maintain heat transfer performance. The seal whisker geometry consists of streamwise and spanwise undulations which reduce the size of the wake and coherent structures shed from the body; a result of an added component of streamwise vorticity along the pin surface. In addition, the vortex shedding frequency becomes less pronounced, leading to significantly reduced lateral loading on the modified cylinder. These whisker geometries are studied for their aero behavior but not from a thermal performance stand point. Hence the main objective of this study is to understand and utilize different flow physics of these whisker geometries in a wall bounded configuration. Computational studies have shown that the modified wake and vortex shedding structures resulting from the geometry tend to reduce the total pressure loss throughout the system without significantly degrading the cooling levels and experimental results agree with these findings. In comparison to a conventional elliptical pin the bio pins have an increase in thermal performance at constant pressure drop by 9% and by 45% in comparison to a conventional cylindrical pin. These findings are important to the gas turbine community and heat exchangers as reduced penalties associated with cooling flows directly translate to improved thermodynamic and propulsive efficiencies.

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