Impact of freestream turbulence on the aerodynamics of a high-speed, low-Reynolds turbine rotor cascade usingWall-Resolved Large Eddy Simulations

Abstract

High-speed low-pressure turbines (HS-LPTs) operate under transonic and low-Reynolds-number conditions, making their boundary layers highly sensitive to transition and separation. Accurate numerical prediction of these effects requires a realistic representation of inflow turbulence, which strongly influences separation, transition onset, and wake development. Conventional turbulence generation methods for internal compressible flows often fail to reproduce experimental turbulence characteristics, leading to significant discrepancies in performance predictions. This study proposes a numerical wind-tunnel replication strategy based on the Dynamic Actuator Line Method (DALM), designed to model the effects of passive turbulence grids commonly used in turbomachinery experiments. The approach generates realistic turbulent inflow conditions without explicitly meshing the grid geometry, significantly reducing computational cost. The method is applied to the SPLEEN C1 transonic cascade, experimentally tested at the von Karman Institute, at Reout,is = 70k and Mout,is from 0.70 to 0.95. Simulations are performed using the YALES2 explicit compressible solver and a wall-resolved LES framework. The DALM successfully reproduces experimental inflow turbulence characteristics: TIx = 2.5% and Λint = 13.5 mm. Accounting for realistic turbulence substantially improves predictions of boundary-layer behavior and wake losses compared to clean inflow conditions. In particular, suction-side separation is delayed, transition occurs earlier, and flow reattachment is promoted at low Mach numbers. Velocity and turbulence statistics in the blade passage and wake show good agreement with PIV measurements, highlighting the importance of realistic inflow turbulence under compressible HS-LPT operating conditions.