Numerical research on rub-impact fault in a blade-rotor-casing coupling system

Abstract

Based on finite element (FE) method, a dynamic model of a single span blade-rotor-casing coupling system is established. The bearings, bladed rotor, discs and casing are simulated using spring-damping element, beam element, shell element and beam element suitable for curved beam separately (the casing stiffness and damping using spring-damping element). The blade-casing rub-impact is simulated using point-point contact elements; here the corresponding nodes of the blades and the casing are identified as the contact points. To deal with contact constraint conditions and simulate blade-casing frictional characteristics, the augmented Lagrangian method and the coulomb friction model are adopted, respectively. The responses of the system are analyzed under two loading conditions by using variable-step Newmark-β integral method combined with Newton-Raphson iteration. The results show that the rub-impact at the second critical speed (case 2) is more serious than that at the first critical speed (case 1). 4× (× denotes the rotating frequency) and its edge frequency components, combination frequency components about 1× can be viewed as distinguishable rub-impact features for cases 1 and 2, respectively. Results can provide theoretical basis for rub-impact diagnosis in blade-rotor-casing coupling systems.