Investigation of Unsteady Aerodynamic Blade Excitation Mechanisms in a Transonic Turbine Stage: Part I — Phenomenological Identification and Classification

Based on the results of time dependent 3D viscous computations the aerodynamic mechanisms that cause the unsteady pressure fluctuations on the vane and rotor blade surface of a high-pressure transonic turbine are identified and separately classified in a phenomenological manner. In order to be able to describe separately the influence of wake, potential and shock distortions on the blade surface pressure at design operation conditions, the stator exit Mach number is increased as to enhance the shock distortions and lowered as to enhance potential and wake distortions. In a comprehensive approach the observations from the off-design conditions are utilized to classify every major perturbation observed in the perturbation space-time maps at design operation conditions. The spanwise variations caused by the inherent 3D nature of the flow field and promoted by the 3D shape of the rotor blade are addressed.