Numerical Study of the Boundary Layer Separation of a Low-Pressure Turbine Cascade at Different Incidence Angles

Modern low-pressure turbine (LPT) pursues high blade loading to improve its efficiency while the possibility of boundary layer separation on the blades is still a challenging problem. The incidence angle is one of the main factors affecting the flow separation and laminar-turbulent transition, which is of key importance for the design of LPT. In this work, based on the initial simulation results obtained using the Reynolds-averaged Navier-Stokes (RANS) method, the flow past a single LPT cascade at three representative incident angles (i=-10°,0°,+10°) is investigated using large-eddy simulation (LES) method with approximately 26 million structured grids. The simulations are carried out with Open Source Field Operation and Manipulation (OpenFOAM) for an off-design low Reynolds number condition Re=40,000 and Ma=0.5. The time-averaged aerodynamic performances and three-dimensional instantaneous flow characteristics of the LPT cascade are discussed in detail, and the results show that the blade loading and the transverse pressure gradient (TPG) from the pressure side to the suction side of leading edge (LE) increase with increasing incidence angle. At the incidence angle of +10°, the LPT cascade undergoes separation and reattachment from the LE to around 20% Cax on the suction surface, which weakens the separation phenomenon at the rear half of the suction surface and the total pressure loss downstream of the trailing edge (TE). It is worth noting that the RANS method underpredicts the blade boundary layer separation region compared with LES under these extreme conditions. These results may offer off-design condition data for the future improvement of RANS models or experimental studies.