Abstract
Aerodynamic interaction of rotor with stator is the primary cause of high cycle fatigue of radial turbine blade. However, few studies have been carried out on aerodynamic interaction in nozzleless radial turbines. This paper studies aerodynamic interaction in a nozzleless radial turbine via the experimentally validated numerical method. The results suggest that several flow phenomena are related to blade excitation. First, when the blade sweeps by the volute tongue, the tongue wake induces a strong separation vortex at the blade leading edge and interacts with it. As the tongue wake migrates downstream, it deforms into a triangular shape across the rotor passage. Second, the potential field of the volute leads to drastic fluctuations of blade load as well as tip leakage flow. Importantly, the tongue wake interacts with the tip leakage vortex in the vicinity of blade trailing edge. This phenomenon results in strong disturbance to pressure fluctuations on suction surface at low pressure ratio, and the frequency of disturbance is roughly one order higher than that of potential field. However, its influence can be neglected at high pressure ratio. Furthermore, the details of vortex evolution in the rotor passage are discussed via the time-space contour plots of pressure difference. Various behaviors including propagation speed, direction, and strength can be well manifested by this method. Finally, the strong influence of unsteady interaction on blade excitation in the nozzleless turbine is confirmed by a direct comparison of blade loads in unsteady conditions with that in quasi-steady conditions.
