An Experimental Investigation Studying the Influence of Dimples on a Film Cooled Turbine Blade Leading Edge
AIR FORCE INST OF TECH WRIGHT-PATTERSON AFB OH SCHOOL OF ENGINEERING AND MANAGEMENT
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An investigation was conducted to examine the effect of a row of cylindrical surface dimples in reducing the heat load on a turbine blade leading edge model. The models consisted of a foam cylindrical leading edge with a flat afterbody fabricated from Plexiglass. A single coolant hole was located 21.5 degree from the leading edge, angled 20 degree to the surface and 90 degree from the streamwise direction. The leading edge diameter to hole diameter ratio was Dd 18.7. A row of seven dimples was placed upstream of one of the coolant holes. Infrared thermography techniques were used to determine the adiabatic effectiveness, eta, and heat transfer coefficient, h, distributions so that the net heat flux reduction could be calculated. Freestream conditions consisted of Reynolds numbers of 60,000 and 30,000 at both low turbulence and high turbulence. At Re 60k, the dimples proved to increase the area averaged eta by an average of 0.007, while the dimpled cases performed equally, if not slightly poorer, than a smooth surface at the lower Reynolds number. The heat transfer coefficient was not greatly affected by the presence of the dimples beyond an xd location of 0.5. Because the heat transfer coefficient remained relatively unchanged while eta increased at Re 60k, the area averaged net heat flux reduction was increased slightly, by an average of 0.02, for the cases with dimples at those freestream conditions. Although, the dimpled cases provided slight improvement to the adiabatic effectiveness for some cases, any advantage was generally less than the uncertainty, indicating that the dimples effect was negligible.
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