PIV Investigation of the Effect of Freestream Turbulence Intensity on Film Cooling From Fanshaped Holes
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The coolant jet structure of fanshaped film cooling holes is experimentally investigated using two-dimensional particle image velocimetry (PIV). These results are coupled with detailed film cooling effectiveness distributions to directly relate the jet structure to surface phenomena. The cooling performance of simple angle, fanshaped holes ( = 35, = 10) is considered. The results from these shaped holes are compared to those from a traditional simple angle, cylindrical hole ( = 35). The flow measurements were performed in a low speed wind tunnel where the freestream turbulence intensity was varied up to 12.5%. The blowing ratio was varied from 0.51.5 to compare the jet structure of relatively low and high momentum cooling flows. Time averaged velocity maps of the coolant flow (in the streamwise direction) were obtained on three planes spanning a single hole: the centerline of the hole, the edge of the cylindrical section of the hole (0.5D), and the edge of the shaped portion of the hole (0.94D). From the seeded jets, time averaged, mean velocity distributions of the film cooling jets were obtained near the cooled surface. In addition, turbulent fluctuations were obtained for each flow condition. Combining the detailed flow field measurements obtained using PIV with detailed film cooling effectiveness distributions on the surface (PSP), provides a more complete view of the coolant jet mainstream flow interaction. Due to the reduced momentum of the coolant, the shaped holes provide improved protection of the flat plate compared to the cylindrical holes. With the reduced velocity of the coolant from the shaped holes, additional turbulent mixing between the freestream and the coolant occurs. However, the increased turbulence does not induce significant changes to the jet structure nor to the surface protection offered by the coolant. Furthermore, the robustness of the fanshaped design is demonstrated through the presentation of time averaged turbulence quantities across the span of the cooling jet.
