Compressible LES of unsteady boundary layer separation and reattachment in turbines: Influence of incidence angle

In order to predict and analyze the phenomenon of separation, reattachment as well as separation bubble at different incidence angles. Self-developed large eddy simulation (LES) program of compressible N-S equations was used to simulate the flow field and the evolutionary process of the boundary layer in TI06A low-pressure turbine cascade. The outlet Mach number is 0.4 and the Reynolds number is 1.1×10⁵ based on the exit isentropic velocity and the axial chord length. The computational results show the time-averaged pressure coefficient on the blade surface and the points of separation and reattachment at +7.8° incidence angle compare well with experiment data. The boundary layer separates from the suction side and the hairpin vortexes are formed in succession. The rapid growth of the hairpin vortex eventually leads to transition in boundary layer. As the incidence angle changes from positive to negative, the separation point on the suction side moves downstream and the length of the separation bubble is gradually shorter.