Blade Excitation Alleviation of a Nozzleless Radial Turbine by Casing Treatment Based on Reduced-Order Model

High cycle fatigue (HCF) is the most common form of blade failure in nozzleless radial turbines. Current studies relating to blade vibration reduction focus on redesign of blade and volute geometries. These methods have the drawbacks of time-consuming, performance sacrifice and lack of generalizability. This paper investigates a novel flow control method for blade vibration reduction without sacrificing the aerodynamic performance based on a reduced-order model. First, the mechanism of the blade excitation is studied by the numerical method validated by experimental measurement. It is confirmed that the blade excitation is triggered by different mechanism between low- and high-pressure ratios. An equivalent excitation pressure is proposed to quantitatively evaluate vibration behaviors of the turbine blade. Based on the mechanism, a reduced-order model is developed to predict the equivalent excitation pressure at high pressure ratio when the excitation is triggered mainly be the disturbance of potential flow field. The method of casing treatment is proposed inspired by the reduced-order model and then optimized to attenuate the blade vibration. The experiment is carried out for the validation of the method and results show that the displacement of the vibration is reduce by 48% by this new method.