STUDY ON BLADE VIBRATION ALLEVIATION IN A NOZZLELESS RADIAL TURBINE VIA CASING TREATMENT

High cycle fatigue (HCF) is the most common form of blade failure in nozzleless radial turbines. Current studies related to blade vibration alleviation focus on redesign of blade and volute geometries. These methods have the drawbacks of long period, performance sacrifice and poor universality. This paper investigates a novel flow control method for blade vibration alleviation based on casing treatment. Fluid-structure interaction (FSI) numerical method validated by experiments is employed. Inspired by the generalized force method, the aerodynamic excitation force caused by volute can be offset by introducing additional excitation force artificially. Axial grooves are designed on the casing in the vicinity of blade trailing edge to achieve this target. Firstly, the influence of relative position of volute tongue and grooves on blade excitation is investigated. It's found that the vibration amplitude is evidently reduced by maximizing the distance between the tongue and the adjacent groove. Generalized force analysis and flow field analysis reveal that the excitation effects caused by volute and casing treatment cancel each other out in this relative location. Next, the influence of configuration parameters of grooves on blade excitation is investigated. Two of the parameters only influence the length of generalized force caused by grooves rather than the phase, which greatly facilitates the design of casing treatment to achieve minimum vibration response. Finally, the effect of optimum design of casing treatment under various working conditions is investigated. The optimum design has good effect at high pressure ratio, which is going to be further optimized to improve its adaptability.