Experimental Studies on Unsteady Aerodynamic Loss of a High-Pressure Turbine Cascade

Abstract

The objective of this study is to investigate how the wake passage impacts the aerodynamic performance of turbine rotor blades in turbomachines. Despite a number of research activities, information on aerodynamic loss generation in turbine rotors under the influence of unsteady flows encountered in actual turbomachines is still limited. This paper describes our newly started research project which aims to gain insight into the physics of the aerodynamic interaction between turbine rotors and incoming periodic wakes, and to establish a method for evaluation of unsteady aerodynamic losses of turbine rotors generated by the wakes. In this study, using a linear turbine cascade and a wake generator, the wake-affected flow field upstream and downstream of the cascade is measured in detail with a five-hole pneumatic pressure tube and a hot-wire probe in order to obtain time-averaged as well as time-resolved characteristics of the flow field. It is accordingly found that the wake passing affects the flow field around the turbine cascade, which yields considerable change in the two-dimensional cascade loss as well as in the secondary vortex structure. Moreover, it is also revealed that a so-called negative jet effect associated with the wakes plays an important role in unsteady loss generation of the turbine cascade, which is in contradiction to the findings by Hodson and Dawes (1996).