Research on dynamic characteristics of three-dimensional tip clearance with regard to blade crack depth and location of rotary blade-disk-shaft coupling system

The rotary blade-disk-shaft (RBDS) coupling system is the core part of the aero-engine and gas turbine, and blade crack is one of the most common faults for the RBDS system. First, to analyze the fault mechanism of blade crack and to investigate the effects of blade crack on the three-dimensional blade tip clearance (3D-BTC) of RBDS system, a novel dynamic model of the RBDS system with the blade crack is developed based on the continuum theory. In this model, the blade radial deformation, flap-wise bending, and chordwise bending are comprehensively considered. Then, combining the blade breathing crack model based on the three-dimensional stress state of the blade, the dynamic model of the RBDS system with blade crack is developed so that the 3D-BTC of blade crack can be obtained. The dynamic model is validated by comparing it with the finite element model and experiments. Besides, based on the analysis of the 3D-BTC dynamic response of RBDS system, the 3D-BTC difference vectors of RBDS system are proposed and the effects of blade crack on the 3D-BTC difference vector are investigated. The simulation results show that the largest element of the 3D-BTC difference vectors indicates which blade is cracked. The largest element of the 3D-BTC difference vector increases with the blade crack depth, and it changes non-monotonically as the blade crack location moves from the blade root toward the blade tip. At last, the 3D-BTC of RBDS system with blade crack is obtained based on the optical-fiber-based measurement system, and the 3D-BTC difference vectors are constructed. The experimental results show that the variation trends of the largest elements of the 3D-BTC difference vectors are consistent with the simulation results, which indicates that the 3D-BTC difference vectors can be applied in the blade crack fault diagnosis of the RBDS system.