Dynamic Strain Reconstruction of Rotating Blades Based on Tip Timing and Response Transmissibility

Dynamic strain of rotating blades is critical in turbomachinery health monitoring and residual life evaluation. Though the blade tip timing (BTT) technique is promising to replace traditional strain gages, the lack of effective strain transformation through BTT hinders the implementation. In this paper, a noncontact dynamic strain reconstruction method of rotating blades is proposed based on the BTT technique and response transmissibility. First, the displacement-to-strain transmissibility (DST) considering rotational speed is derived from the frequency response functions based on blade mode shapes. A quadratic polynomial function of DST with respect to the rotational speed is provided to calibrate DST in blade rotational state. Second, the blade-tip displacement in resonance is obtained by BTT measurement and the Circumferential Fourier Fit processing method. Third, the dynamic strains of critical points on blades are calculated using the DST in conjunction with the tip displacement amplitude. In this paper, to validate the proposed method, acceleration and deceleration experiments, including both BTT and strain gages, are conducted on a spinning rotor rig. Experimental results demonstrate that the reconstructed dynamic strains of different positions on the rotating blades correspond well to the results measured by strain gages. The mean relative error between the reconstructed and measured results is generally within 8%.