Response of Transitional Boundary Layers Over Low-Pressure Turbine Blades to Varying Characteristics of Free-Stream Turbulence

Recent research conducted by the VKI on high-speed low-pressure turbines (LPTs) employed the SPLEEN C1 cascade, a geometry representative of a rotor hub in modern high-speed LPTs. To facilitate continued investigation of flow physics, an equivalent low-speed version of the SPLEEN C1 blade profile is designed. The performance of this blade design, subjected to varying free-stream turbulence (FST) characteristics, is explored in this paper employing wall-resolved Large Eddy Simulations. Two FST intensity values — 2.4% and 10.2% are studied with the integral length scale varying from 0.125–0.25 times the blade pitch. The operation Reynolds number for this configuration is Reexit,is = 80,000. The flow behavior over the blade is examined with the aid of instantaneous flow features and time averaged flow statistics. The high-fidelity simulations are further complimented by Reynolds Averaged Navier-Stokes simulations that provide additional data to compare loading and wall-shear distribution over the blade. The boundary layer over this blade design is mostly laminar and is devoid of any separation bubble. It is observed that the aft portion of the blade suction side and front portion of the blade pressure side are sensitive to the FST characteristics. It is revealed that an increasing FST intensity tends to accelerate the transition process on the suction surface close to the trailing edge and the influence of larger integral length scales in this process is enhanced at high FST intensities. Furthermore, the distribution of turbulent kinetic energy and wake loss coefficient show that the losses are enhanced with an increase in the FST intensity.