Dynamic Characteristics Analysis of 3D Blade Tip Clearance for Turbine Blades with Typical Cracks

Abstract

As well known, the crack is a typical fault of turbine blades, which is difficult to detect due to the weak fault features contained in the rotor vibration. Although some fault diagnosis methods based on blade tip timing (BTT) are proposed to detect blade cracks, the limited fault features can be extracted because the BTT signals contain only one-dimensional fault information. Based on the dynamic analysis, the cracked blade undergoes three-dimensional (3D) deformation so that it would be reflected in the changes of the three-dimensional blade tip clearance (3D-BTC). Therefore, the dynamic characteristics of the 3D-BTC of turbine blades with typical cracks should be investigated to obtain its change rule and achieve a more comprehensive diagnosis of blade cracks. In this paper, the 3D finite element model of the turbine blisk is established, and the fluid-thermal-solid coupling analysis is implemented to calculate the blade deformation. Then, a novel dynamic computation method is proposed to calculate the 3D-BTC based on the blade deformation. The typical blade cracks are taken into consideration, and the dynamic characteristics of the 3D-BTC regarding the typical cracks are analyzed to obtain its change rule. The results show that abundant crack fault information can be obtained based on the 3D-BTC, which can facilitate the comprehensive diagnosis of turbine blade cracks.