| An important method of increasing both the power output and thermal efficiency ofgas turbines is to elevate the mainstream gas inlet temperature. The technology ofcooling gas turbine components must be improved as metal should withstand exposureto the mainstream gas. Internal cooling is one of the essential cooling methods for vanesand blades of high pressure turbine. The friction loss of internal cooling structuresaffects the flowrate distribution of the blade, while the heat transfer of internal coolinghas an impact on the blade temperature. Thus, it’s important to measure the exact valueof these two factors. The heat transfer and flow field of internal cooling structures isdominated by boundary layer separation and reattachment, large seperations, as well asconjugate heat transfer. Understanding these mechanisms is also important for thetheoretical research. In this thesis, the heat transfer development near the inlet, effects oflateral ejection on heat transfer and flowfield, interactions between pin fin andimpingement inside the trailing edge region of gas turbine blade is studied. As heattransfer enhancement often results in larger pressure drop, the relationship between heattransfer, flowrate and friction loss of typical internal cooling structures is alsoinvestigated.An uncertainty analysis was done for the transient liquid crystal method. Using thenon-dimensional temperature distribution analysis, systematic error of mainstreamreference temperature can be reduced, and Nu (Nusselt number) can be adjusted by15%.The uncertainty of transient liquid crystal method is related with the range of parameters.Low mainstream temperature will result in greater error, thus must be avoided. Theuncertainty for Nu measurement in the current experiments is±10%.The heat transfer distribution of trailing edge ribbed channel changes with inlet andoutlet conditions. For a fully developed flow field condition, heat transfer inside asquare-cross-sectioned channel is dominated by the secondary flow patterns of differentrib configurations. The peak Nu during the heat transfer development is20%~70%higher than that when heat transfer is fully developed, thus the development process isimportant for short channels. Lateral flow at the outlet results in non-uniform Nudistribution: The local Re(Reynolds number) and Nu decreases streamwisely as moreand more coolant is drawn out of the channel. A corner vortex with low heat transfer level appears at the end of the channel as streamlines bend towards the exit holes. Heattransfer distribution is changed by moving the center of V-shaped rib or adding localimpingement holes. The Nu is largest for the configuration using symmetry V-shapedribs with the ratio of rib pitch to rib height equal to10.For a channel with pin fins, average Nu will increase by20%~50%while usingimpingement at the inlet. However, f(friction factor) also increases4~20times. The Nunear the stagnation point of the jet increases2~3times, and the pin fins can elevate theheat transfer area. Thus under conjugate conditions local temperature near thestagnation point will be low and the thermal stress can increase. The open flow arearatio of impingement holes and pin fins, and the relative locations between jets and pinfins all have an important impact on heat transfer and friction loss.By collecting and analyzing the data of different internal cooling structures, it canbe found that the Re, f and Nu has staticticaldependence. For flow inside artificialroughened channels, a correlation based on exponential function can calculate Nu undercertain Re and f with an uncertainty of30%~40%. The Nu increases with increasing Reand f, but fincreases much faster than Nu. |
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