Experimentally Observed Unsteady Work at Inlet to and Exit From an Axial Flow Turbine Rotor

World literature has introduced the aerodynamic importance of unsteadiness in turbines. In particular the unsteady static pressure field determines the work of the machine. The unsteadiness can redistribute the total pressure in a cascade with wake interaction. It has been shown that differences in work between wake and free-stream can act to rectify the wakes and boost efficiency. In this paper FRAP (Fast Response Aerodynamic Probe) data is used to study the nature of the unsteady work in the flow at entry to and exit from a rotating turbine blade. The topic is addressed experimentally, theoretically and computationally. It is found at both rotor inlet and exit that upstream wakes influence the unsteady work distribution. The relationship between the unsteady work in the absolute frame, the relative frame and the momentum of the fluid circumferentially is derived and verified experimentally. Computational results (URANS) are compared to the experimental results: reasonable agreement is found at rotor exit but significant differences at rotor inlet are found. The CFD has failed to capture the von Karman vortices and has dramatically lower levels of unsteady work. The experimental unsteady work distribution suggests possible effects of wake bending and vortex instability.