关键词: 航空发动机;涡轮;叶型;分离流;转捩流;大涡模拟

Abstract: Three-dimensional large eddy simulation(LES) of separated flow transition on a highly-loaded low-pressure turbine profile under steady inflow conditions was performed using the dynamic subgrid-scale model.The Reynolds number based on inlet velocity and axial chord length is 5×104,with a free turbulence inflow,and the flow is incompressible.The comparisons of simulated mean quantities with the available experimental data show that the mean bubble length and thickness are a little under-predicted.Because of numerical errors,the freestream turbulence intensity near the profile leading edge is found to be about 0.22%,which triggers the inviscid Kelvin-Helmholtz instability in the free shear layer after separation.The initial two-dimensional instability Kelvin-Helmholtz mechanism grows downstream slowly and linearly,and it induces the formation and shedding of two-dimensional spanwise vortices at some streamwise location where the instability becomes three dimensional and begins to grow quickly and nonlinearly.In the process of vortex shedding,the spanwise vortices become stronger,being more and more severely distorted under the nonlinearly-growing three-dimensional motions,ultimately leading to the flapping free shear layer rolling up in their strongest state,forming the large-scale vortices which eventually break to full turbulence around the mean reattachment location under significant growth of three-dimensional motions.The structures of streamwise vortices are obviously detected at the late stage of transition.

Key words: Aircraft engine;Turbine;Blad airfoil;Separated flow;Transition flow;Large eddy simulation+