The performance of a low-pressure turbine (LPT) is strongly influenced by laminar-turbulent transition and boundary layer separation. In the context of aircraft engines, the current design trend is to decrease the blade count in order to reduce weight and costs. Consequently, the blade aerodynamic load is increased, and this may lead to serious boundary layer separation over the suction side. Several authors demonstrated the capacity of passing wakes to reduce losses due to separation and thus to consider higher blade load. These passing wakes coming from the upstream blades induce early boundary layer transition and prevent massive separation. The accurate simulation of this unsteady transition is mandatory to predict losses and performance of a high-lift LPT blade.The present study focuses on the very high-lift T106C cascade with passing wakes. Unsteady Reynolds-Averaged Navier-Stokes (URANS) simulations are carried out and compared to experimental data provided by Von Karman Institute in the context of the European program TATMo. The γ-Reθt transition model of Menter-Langtry coupled with k-ω turbulence model of Wilcox is used to predict laminar-turbulent transition. An unsteady inlet boundary condition is defined from experimental data to generate representative passing wakes. This configuration is simulated with different Reynolds numbers from 80 000 to 250 000 and with three different freestream turbulence intensities.First, this paper compares the numerical results with the experiments to evaluate the γ-Reθt transition model on the T106C cascade with passing wakes. Then, the definition of unsteady inlet condition and wake profile is discussed. The numerical results are in good agreement with the experimental data. Like the experiments, the URANS simulations show a reduction of the time-averaged separation bubble length and of the overall losses in the presence of passing wakes, especially for the lower Reynolds numbers where significant separation appears. Also, the isentropic Mach number distributions and the total pressure deficit downstream of the trailing edge are well predicted. Moreover, the analysis of the time evolution of isentropic Mach number and wall friction around the blade confirms the characteristics of wake-induced unsteady transition induced by wake that have been highlighted in previous studies :&nbsp; periodical length reduction or suppression of separation bubble, calming effect and passing wake convection. &nbsp;To study the effect of wake profile on unsteady transition, the experimental wake profile is modified to vary its width and intensity. This sensitivity study gives some knowledge about the uncertainty of transition mechanism and performances regarding wake profiles.

Simulation of Passing Wakes Inducing Unsteady Boundary Layer Transition Around Low-Pressure Turbine Blade

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2021/volume/84898

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