Date of Award

January 2015

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Mechanical Engineering

First Advisor

Forrest Ames

Abstract

The purpose of this study is to experimentally investigate the effects of high free stream turbulence on shaped hole film cooling and heat transfer in an accelerating boundary layer. Film cooling is one of most widely used techniques in cooling high pressure turbine blades and endwalls, whether they are land based power turbines or those used for aircraft propulsion. In the section immediately after the combustor, there is very high turbulence and acceleration, and adequate cooling must be implemented to ensure that components do not prematurely fail. This study is able to apply high turbulence intensities to a test section whose acceleration profile yields a favorable pressure gradient and allows us to see the real world effects on shaped hole film cooling effectiveness and heat transfer from high turbulence intensities.

The experimentation was conducted in the University of North Dakota large scale low velocity wind tunnel facility. A total of six well documented turbulence intensities ranging from 0.7% to 13.7% were implemented on a large cylindrical test surface at Reynolds numbers of 250,000 and 500,000 and four blowing ratios. The low Reynolds number setup used blowing ratios of M = 0.55, 0.97, 1.35, and 1.89, while only the lowest two blowing ratios were tested at the high Reynolds number. The six turbulence intensities were achieved using a low turbulence (LT) nozzle (Tu = 0.7%), the LT nozzle with a small grid at two locations (Tu = 3.5% and 7.8%), the LT nozzle with a large grid (Tu = 8.1%), and a mock aero combustor with and without a decay spool (Tu = 9.3% and 13.7%). The shaped holes leading edge insert was designed to provide full coverage with two staggered rows of holes with 8º lateral expansion. Both rows of holes are introduced to the surface at 30º.

Data showed turbulence to be detrimental to shaped hole film cooling effectiveness in all cases, and to increase heat transfer as the early onset of transition was amplified. The low Reynolds number showed improved film cooling effectiveness over the high Reynolds number due to a longer transition region and slower boundary layer growth. Comparisons of shaped hole film cooling to previous slot film cooling data show the slot to have similar performance in the latter half of the test surface. However, heat transfer and adiabatic effectiveness were much higher in near region due to the slot’s superior coverage. IR camera measurements of shaped hole film cooling show the coolant coverage of the surface at the two low blowing ratios, giving a better perspective on the behavior of the coolant jets after ejection. These data should be useful for comparison in future studies.

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