Separated boundary layers of the low pressure turbine blade suction surface under wall heat transfer and pressure gradient conditions are investigated using large eddy simulations (LES) in this paper. The study constructed a converging-diverging channel with a flat plate as the bottom wall, and the pressure distribution of the bottom wall is similar to that of a high lift low pressure turbine blade suction surface. The boundary layer was investigated under different heat transfer boundary conditions of the bottom wall (i.e., the adiabatic wall and the isothermal wall with the wall temperature being 0.8 times of the inflow temperature). The time-averaged flow parameters and the separation bubble characteristics were analyzed and discussed. The evolution of coherent structure diagrams of the boundary layer was also obtained to study the evolution process of the vortex. The results show that the cooled isothermal wall condition can significantly suppress the separation bubble and reduce the frequency of the large scale spanwise vortex roll-up. Under the two wall heat transfer conditions, the scale of the near wall small scale spanwise vortex is similar as well as the scale of the large scale spanwise wortex. The location of the vortex are also approximate under the two wall heat transfer conditions, but the position of the large scale spanwise vortex shedding from separated laminar boundary layers moves upstream under the cooled isothermal wall condition, and the transition process is more rapid than that of the adiabatic wall condition.

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