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Blade Tip Film– Cooling and Heat Transfer |
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Project Funded by: Pratt & Whitney |
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Sealing and durability for turbine blade tips, as illustrated in Figure 1, have been challenging problems since the development of gas turbine engines. Blade tip designs are extremely important in terms of sealing and engine performance. In general, overall engine performance can be improved by increasing turbine inlet temperatures. This must be done, however, without sacrifice of part life. As a result, cooling methods along the blade tip need to be devised and applied effectively. Film-cooling is typically used as a blade tip cooling method, whereby coolant is supplied through holes placed along the pressure side of a blade. As the leakage flow convects across the tip, so does the coolant injected from the pressure side. |
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Figure 1. Illustration of a blade tip with a clearance gap that allows hot gas to leak. |
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We have ongoing investigations into the leakage over the blade tip and how cooling holes affect the flow over the tip. Our past and current studies are assessing the placement of cooling holes along the pressure side of the blade, near the tip, as shown in Figure 2. Testing is performed in a large-scale, low speed wind tunnel and parallel computational fluid dynamics simulations are also performed. |
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Figure 2. Film-cooling holes along the pressure side tip of a turbine blade. |
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Figure 3 compares the measured adiabatic effectiveness levels along the blade tip for a small and large tip gap at the same coolant flow conditions. For both cases the leading edge region is nearly completely cooled by the dirt purge holes, which are present to expel dirt that is ingested into the engine. The results indicate a dramatic decrease in the surface temperatures (red is hot) for the small tip gap relative to the large tip gap. |
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Figure 3. Measured cooling on a blade tip for a small (left) and large clearance gap. |
