Boundary layer separation, transition and reattachment have been studied on a very high lift, low-pressure turbine airfoil. Experiments were done under high (4%) freestream turbulence conditions on a linear cascade in a low speed wind tunnel. Pressure surveys on the airfoil surface and downstream total pressure loss surveys were documented. Velocity profiles were acquired in the suction side boundary layer at several streamwise locations using hot-wire anemometry. Cases were considered at Reynolds numbers (based on the suction surface length and the nominal exit velocity from the cascade) ranging from 25,000 to 300,000. At the lowest Reynolds number the boundary layer separated and did not reattach, in spite of transition in the separated shear layer. At higher Reynolds numbers the boundary layer did reattach, and the separation bubble became smaller as Re increased. High freestream turbulence increased the thickness of the separated shear layer, resulting in a thinner separation bubble. This effect resulted in reattachment at intermediate Reynolds numbers, which was not observed at the same Re under low freestream turbulence conditions. Numerical simulations were performed using an unsteady Reynolds averaged Navier-Stokes (URANS) code with both a shear stress transport k-ω model and a 4 equation shear stress transport Transition model. Both models correctly predicted separation and reattachment (if it occurred) at all Reynolds numbers. The Transition model generally provided better quantitative results, correctly predicting velocities, pressure, and separation and transition locations. The model also correctly predicted the difference between high and low freestream turbulence cases.
Experimental and Computational Investigations of Separation and Transition on a Highly Loaded Low-Pressure Turbine Airfoil: Part 2 — High Freestream Turbulence Intensity
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Volino, RJ, Kartuzova, O, & Ibrahim, MB. "Experimental and Computational Investigations of Separation and Transition on a Highly Loaded Low-Pressure Turbine Airfoil: Part 2 — High Freestream Turbulence Intensity." Proceedings of the ASME 2008 International Mechanical Engineering Congress and Exposition. Volume 10: Heat Transfer, Fluid Flows, and Thermal Systems, Parts A, B, and C. Boston, Massachusetts, USA. October 31–November 6, 2008. pp. 1213-1225. ASME. https://doi.org/10.1115/IMECE2008-68776
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