Effects of incidence angle on a low-pressure turbine blade boundary layer evolution through large eddy simulation

Abstract

The evolution mechanism of the boundary layer and coherent structures in a low-pressure turbine blade is discussed. Five different incidence angles over the T106A blade for a Mach number Ma = 0.404 and Reynolds number Re = 0.6 × 105 (based on the axial chord and outlet velocity) are performed using large eddy simulation method. The calculation results at +7.8 incidence angle are agreed well with the experimental and direct numerical simulation data. The influence of the incidence angle on the flow field is mainly shown at the front of the suction side and pressure side. As the incidence angle changes from positive to negative, the separation bubble near the leading edge disappears and the blade loading decreases gradually. When the incidence angle reduces to −5°, separation bubble appears near the leading edge of the pressure side. At the case of incidence angle equaling −10°, the length of time-averaged separation bubble on the pressure side grows to 39% axial chord and the evolution process of the coherent structures is extremely complex. The spanwise vortexes roll up near the leading edge and gradually evolve into streamwise vortexes. High-energy fluid in the main flow was driven to near-wall zone by the rotating effect of streamwise vortexes, which increases the fluid momentum inside the boundary layer. The streamwise vortexes are stretched by the strong acceleration of the flow until they transport to the trailing edge.