Session: 34-08 LES Solvers and applications 2

Paper Number: 127182

127182 - Large Eddy Simulations of a High-Speed Low-Pressure Turbine Cascade at Subsonic and Transonic Mach Numbers 

High-Speed Low-Pressure Turbines are one key turbomachinery component in ultra-high bypass ratio geared turbofan engines. The High-Speed Low-Pressure Turbine (HS-LPT) typically operates at transonic exit Mach numbers and low Reynolds numbers. These flow regimes are prone to boundary layer instabilities such as separations on the suction side, leading to a significant increase in losses. It is therefore essential to understand the operation of LPTs and, more specifically, the behaviour of the boundary layer on the blades in such environments.

We present a numerical investigation of a high-speed low-Reynolds turbine cascade simulated at nominal and off-design Mach numbers. The study case is the SPLEEN C1 cascade tested in the transonic linear cascade rig S-1/C of the von Karman Institute. The cascade is numerically operated at the nominal test exit Reynolds number Re_2,is = 70k, over a range of subsonic and transonic exit Mach numbers: M_2,is = 0.70 ; 0.80 ;  0.90 and 0.95. 

All simulations are performed with the Explicit Compressible Solver of the massively parallel code YALES2, using a Wall Resolved Large-Eddy Simulations (WRLES) approach, and featuring a fourth-order finite volume spatial discretization. This scale-resolving approach allows to capture the turbine flow physics with high accuracy at an acceptable computational cost. 

The test case offers the possibility to assess the Mach and compressibility effects on the profile aerodynamics of low-pressure high-speed turbines: separation, transition mechanisms, unsteadiness and passage choking, trailing edge unsteady flows, and entropy generation. 

The flow predictions show a substantial agreement with the available high-fidelity experimental data. However, the calculations suggest that, at Mach numbers above 0.90, the wake thins and loss increases with the Mach number. This evidence is not supported by the experiments. The root cause is likely to be found in the laminar inflow used in the LES simulations compared to the free-stream turbulence intensity level of 2.5 % of the experimental test case. Compressibility effects are observed. In particular, a weak compression wave stands at the cascade throat for the case M_2,is = 0.90, whereas a shock appears for M_2,is = 0.95 with the cascade choked. The role of the shock on the separation and transition on the blade suction side is discussed.

Presenting Author: Patrick TENE HEDJE University of Mons (UMONS), Faculty of Engineering

Presenting Author Biography: Patrick Tene Hedje graduated as mechanical engineer specialized in energy systems in 2020 at the Faculty of Engineering of the University of Mons/Belgium. He then worked as a researcher on a project involving numerical simulations of wind turbines for 1 year within the Fluids-Machines unit of the same Faculty. In 2022, he began his PhD in the same unit, focusing on the CFD of low-pressure turbines, in collaboration with the von Karman Institute for Fluid Dynamics in Belgium.

Authors:

Patrick TENE HEDJE University of Mons (UMONS), Faculty of Engineering
Laurent Bricteux University of Mons (UMONS), Faculty of Engineering
Yacine Bechane INSA,University of Rouen
Sergio Lavagnoli von Karman Institute for Fluid Dynamics