Large eddy simulation of unsteady transitional flow on the low-pressure turbine blade

Abstract

The aim of this paper is to predict the phenomenon of laminar separation, transition and reattachment in a low-pressure turbine (LPT). Self-developed large eddy simulation program of compressible N-S equations was used to describe the flow structures of T106A LPT blade profile at Reynolds number of 1.1×105 based on the exit isentropic velocity and chord length. The computational results show the distributions of time-averaged wall-static pressure coefficient and mean skin-friction coefficient on the blade surface. The locations of laminar separation and reattachment points occur around 87% and 98% axial chord, which agree well with experiment data. The two-dimensional shear layer is gradually unstable along the downstream half of the suction side as a result of the spanwise fluctuation and the roll up of shear layer via Kelvin-Helmholtz (KH) instability. Three-dimensional motions appear near 84% axial chord which later triggers spanwise vortexes and streamwise vortexes, leading to transition to turbulence in the separation bubble. Through introducing the concept of dissipation function, the high loss mainly comes from the places where strong shear layer and intense fluctuation exist. Furthermore, the separation region is only an accumulation center of the low-energy fluid rather than an area of loss source.