Heat transfer experiments were done on a flat plate to study the effect of internal counter-flow backside cooling on adiabatic film cooling effectiveness and heat transfer coefficient. In addition, the effects of density ratio (DR), blowing ratio (BR), diagonal length over diameter (L/D) ratio, and Reynolds number were studied using this new configuration. The results are compared to a conventional plenum fed case. Data were collected up to X/D =23 where X=0 at the holes, an S/D = 1.65 and L/D=1,2. Testing was done at low L/D ratios since short holes are normally found in double wall cooling applications in turbine components. A DR of 2 was used in order to simulate engine-like conditions and this was compared to a DR of 0.92 since relevant research is done at similar low DR. The BR range of 0.5 to 1.5 was chosen to simulate turbine conditions as well. In addition, previous research shows that peak effectiveness is found within this range. Infrared (IR) thermography was used to capture temperature contours on the surface of interest and the images were calibrated using a thermocouple and data analyzed through MATLAB software. A heated secondary fluid was used as 'coolant' in the present study. A steady state heat transfer model was used to perform the data reduction procedure. Results show that backside cooling configuration has a higher adiabatic film cooling effectiveness when compared to plenum fed configurations at the same conditions. In addition, the trend for effectiveness with varying BR is reversed when compared with traditional plenum fed cases. Yarn flow visualization tests show that flow exiting the holes in the backside cooling configuration is significantly different when compared to flow exiting the plenum fed holes. We hypothesize that backside cooling configuration has flow exiting the holes in various directions, including laterally, and behaving similar to slot film cooling, explaining the differences in trends. Increasing DR at constant BR shows an increase in adiabatic effectiveness and HTC in both backside cooling and plenum fed configurations due to the decreased momentum of the coolant, making film attachment to the surface more probable. The effects of L/D ratio in this study were negligible since both ratios used were small. This shows that the coolant flow is still underdeveloped at both L/D ratios. The study also showed that increasing turbulence through increasing Reynolds number decreased adiabatic effectiveness. / MS / Gas turbine engines are used for multiple applications for power (power plants) or thrust (aircraft propulsion). Engine efficiency is correlated with higher working temperatures, which exceed the melting points of the materials being used. Therefore, more efficient cooling techniques are needed in order to protect the engine turbine components, such as blades and vanes. Relatively cooler air is bypassed from the compressor to the turbine section to cool the turbine components from the high temperatures. The air flows through the turbine components and out through machined holes referred to as film cooling holes. A protective layer, or film, protects the external region of the blade or vane. Previous research has found that the geometry of the airfoils used and the flow conditions play a major role in heat transfer. Most of the relevant research use a model that contains one-sided heat transfer. The present study focuses on combined backside and film cooling heat transfer, with different geometries and flow conditions, using a steady-state model for the data reduction procedure.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/97010 |
| Date | 30 August 2018 |
| Creators | La Rosa Rivero, Renzo Josue |
| Contributors | Mechanical Engineering, Ng, Wing Fai, Mahan, James R., Dancey, Clinton L. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf, application/vnd.openxmlformats-officedocument.wordprocessingml.document |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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