Predicting High Lift Low Pressure Turbine Cascades Flow Using Transition Sensitive Turbulence Closures

Abstract

This paper discusses the application of different transitionsensitive turbulence closures to the prediction of lowReynoldsnumber flows in highlift cascades operating in lowpressure turbine (LPT) conditions. Different formulations of the well known خ³Rثœeخ¸t model are considered and compared to a recently developed transition model based on the laminar kinetic energy (LKE) concept. All those approaches have been coupled to the Wilcox kد‰ turbulence model. The performance of the transitionsensitive closures has been assessed by analyzing three different highlift cascades, recently tested experimentally in two European research projects (Unsteady Transition in Axial Turbomachines (UTAT) and Turbulence and Transition Modeling for Special Turbomachinery Applications (TATMo)). Such cascades (T106A, T106C, and T108) feature different loading distributions, different suction side diffusion factors, and they are characterized by suction side boundary layer separation when operated in steady inflow. Both steady and unsteady inflow conditions (induced by upstream passing wakes) have been studied. Particular attention has been devoted to the treatment of crucial boundary conditions like the freestream turbulence intensity and the turbulent length scale. A detailed comparison between measurements and computations, in terms of blade surface isentropic Mach number distributions and cascade lapse rates will be presented and discussed. Specific features of the computed wakeinduced transition patterns will be discussed for selected Reynolds numbers. Finally, some guidelines concerning the computations of highlift cascades for LPT applications using Reynoldsaveraged Navier–Stokes (RANS)/unsteady RANS (URANS) approaches and transitionsensitive closures will be reported.