Date of Award

3-24-2016

Document Type

Thesis

Degree Name

Master of Science

Department

Department of Aeronautics and Astronautics

First Advisor

James L. Rutledge, PhD.

Abstract

Film cooling scheme development for use in gas turbine engines often entails the characterization of adiabatic wall temperature distributions in order to determine the driving temperatures for the convective heat transfer processes in the engine. For convenience, adiabatic effectiveness experiments are often performed near room temperature and presumed to scale the engine condition. In order to perform these experiments, researchers elect to match the freestream Reynolds number to that of the engine. When scaling to engine temperatures, however, coolant and freestream fluid properties both change nonlinearly. Therefore the ratio of these properties does not remain constant as the temperature changes. The density ratio change has the greatest effect though dynamic viscosity, specific heats, and thermal conductivities are also temperature dependent. These changes in fluid properties result in an inability to match the freestream and coolant Reynolds numbers, the mass flux ratio, momentum flux ratio, and other parameters simultaneously between laboratory and engine conditions. The effects of various coolant flow rate parameters and fluid transport property ratios on the adiabatic effectiveness distribution for a simulated leading edge were evaluated using both binary PSP and infrared thermography methods with a low thermal conductivity model at a freestream Reynolds number of 60,000. PSP was used to decouple the mass and momentum transport from the thermal transport in the film cooling process as well as avoid the measurement uncertainties due to conduction into the model. The coolant gases evaluated in this study were air, argon, carbon dioxide, and nitrogen. The test geometry was a semi-cylinder with flat afterbody with a single 90° compound angled cylindrical coolant hole located 21.5° from the stagnation line and angled 20° to the surface. No single flow rate parameter was found to completely scale the effects of the coolant properties, though momentum flux ratio was found to best scale the shape and location of the adiabatic effectiveness distribution while the advective capacity ratio was found to scale the effectiveness magnitude between coolants at matched momentum flux conditions in thermal experiments. Further, comparison of the thermal and PSP results indicated that the thermal influence of the coolant plume does not necessarily follow the actual placement of the coolant jet on the model surface and is subject to more diffusive processes than the mass transfer analogy would indicate, exposing a potential flaw in the direct application of PSP results to gas turbine heat transfer evaluations.

AFIT Designator

AFIT-ENY-MS-16-M-245

DTIC Accession Number

AD1054205

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