Transition Modelling For Flow Separation In Low-Pressure Turbine Cascades

Abstract

Low-pressure turbine (LPT) blades at high altitude present complex flow situations due to presence of separation and subsequent transition. These relatively low Reynolds number flows are challenging to simulate in a computationally affordable framework. Present work addresses this issue by providing solutions of such LPT flows using Reynolds-averaged Navier-Stokes (RANS) simulations. The simulations are performed on a cascade with Pratt & Whitney blade T106A. Simulation conditions are based on the experiments carried out at a transitional Re = 51,831 at a relatively high angle of incidence of 45.5°. Simulations were performed using several turbulence and transitional models. The computed results are compared with the experimental data as well as available Direct Numerical Simulation (DNS) results. All three turbulence models used for the study- Spalart-Allmaras (SA), k-ω SST and Realizable k-є - predict the flow well on the pressure side of the blade but fail to capture the flow on the suction side due to involvement of separation and transition. However, when these simulations are performed with transition models (γ-Reθ and the laminar kinetic energy (LKE)) on the same grid, significant improvements were seen in the prediction of the separation region. Both the models predicted the pressure plateau near the trailing edge of the suction side related to the separation region. A detailed flow analysis, further, suggests that compared to the γ-Reθ model, the LKE model reproduces the separation bubble structure more accurately, close to that obtained from high-resolution direct numerical simulations in the literature.