Analysis of the effects of upstream turbulence on aircraft engine turbine blades

The effects of upstream turbulence on the heat transfer and aerodynamics of aircraft turbine blades are investigated numerically. The numerical simulation provides a tool for generating data that could be used to enhance the understanding of the complicated flow and thermal conditions under which a turbine blade operates. These conditions are difficult to investigate experimentally. The numerical procedure uses a curvilinear finite difference method to perform a direct numerical simulation of the flow and heat transfer around the blade. Validation of the procedure is done by comparisons with experiments carried out at the Texas A&M University, College Station, Texas.; The results indicate that the flow field around the blade is influenced by both the geometry of the blade as well as apparent blowing/suction effects from adjacent blades. The suction side of the blade mainly undergoes adverse pressure gradient flow with the exception of a small section of the trailing edge in which the presence of the adjacent blade above causes a slightly favorable pressure gradient for x/C > 0.9. In all the cases studied, the flow around the blade is approximately laminar but separated at the lowest Reynolds number studied (Re = 50,000). At the higher Reynolds numbers (Re = 100,000 and Re = 200,000), transition occurs and appears to prevent separation. In general, regions of the blade undergoing adverse pressure gradient are sensitive to upstream turbulence. This is also the region where separation occurs for the lowest Reynolds number case. Upstream turbulence promotes early transition which in turn prevents the occurrence of separation, as no separation is observed for all cases in which transition onset is initiated. Transition is found to occur naturally at the most receptive region of the blade on the suction side and the effect of upstream turbulence is to move the transition point upstream and the resulting disturbances to amplify more quickly. Regions under favorable pressure gradient, mostly on the pressure side, are found to be less receptive to the effects of upstream turbulence. These regions do not experience natural transition at the lowest Reynolds numbers investigated in the present work. Results from the turbulence kinetic energy budgets show an increase in the production term within the transition region (on the suction side) relative to the other regions around the blade surface. Application of upstream turbulence is found to enhance the heat transfer around the blade surface. This enhancement is observed even for the lowest Reynolds number case where the flow around the blade remained laminar.