Blade–Row Interactions in a Low Pressure Turbine at Design and Strong Off Design Operation

Abstract

In a joint project between the Institute of Aircraft Propulsion Systems (ILA) and MTU Aero Engines, a twostage low pressure turbine is tested at design and strong offdesign conditions. The experimental data taken in the Altitude Test Facility (ATF) aims to study the effect of positive and negative incidence of the second stator vane. A detailed insight and understanding of the blade row interactions at these regimes is sought. Steady and timeresolved pressure measurements on the airfoil as well as inlet and outlet hotfilm traverses at identical Reynolds number are performed for the midspan streamline. The results are compared with unsteady multistage computational fluid dynamics (CFD) predictions. Simulations agree well with the experimental data and allow detailed insights in the timeresolved flowfield. Airfoil pressure field responses are found to increase with positive incidence whereas at negative incidence the magnitude remains unchanged. Different pressure to suction side (SS) phasing is observed for the studied regimes. The assessment of unsteady blade forces reveals that changes in unsteady lift are minor compared to changes in axial force components. These increase with increasing positive incidence. The wakeinteractions are predominating the blade responses in all regimes. For the positive incidence conditions, vane 1 passage vortex fluid is involved in the midspan passage interaction, leading to a more distorted threedimensional (3D) flow field.