Blade tip timing (BTT) measurement technology is more widely used to determine the vibrational stress of rotating blades and play an important role for blade service life prediction. The dynamic blade displacements can be measured by tip timing sensors, and then be converted to blade stress by the modal shape information from finite element method (FEM) analysis. However, there are always two uncertainties between the measured displacements by BTT and the modal shape by FEM analysis. First, the effective positions detected by sensors may shift from where they expected due to the deformation of the blade. This deviation may yield calibration factors with deceptions, which will present an inaccurate correlation for the blade stress level and the tip displacement. Second, when vibrating, blade tip would actually oscillate around the equilibrium position both in circumferential and axial direction, while the sensors can only detect the movements along the circumference direction and neglect the other. This causes the measured displacements to be different from the actual displacements. To deal with these two problems, a novel method based on the vibration amplitudes of blade tip along axial direction is proposed to identify the effective detected position. The vibration stress of the whole blade then can be determined by linking the modified displacements to the mode shape information from finite element (FE) predictions. This method is validated by a numerical BTT simulator, which is trying to simulate the actual testing process of BTT measurement. Both synchronous and asynchronous vibrations are discussed to illustrate the applicability of this method. Moreover, sensitivity analysis is performed to identify the uncertainties from the vibration amplitude and mode shape inaccuracies. Results demonstrate the great potential of the method for vibration stress determination.

In recent years, hollow fan blades have been widely used to meet the requirements of aeroengines for lightweight and better performance. However, the hollow fan blade will change from the manufacture shape to the operating shape with large deformations during operation. This deviation, if neglected, will lead to deceptive results for structural and aerodynamic analysis. However, the existing methods have low prediction accuracy or require a lot of calculation in case of large deformations. In this paper, an iterative method for parametric modeling, automatic generation of finite element model, and hot-to-cold analysis of an H-shaped hollow fan blade are proposed. The accuracy and efficiency of the traditional uncoupling (UCM) and weak coupling methods (WCS), as well as the proposed strong–weak coupling method (SWCS), are compared with the strong coupling method (SCU) as a reference. Results show that improvements in the prediction accuracy can be made by the SWCS method, and the error of the maximum blade deformation is 2.3%, while the error of the UCM method and WCS method is 30% and 12%, respectively. An excellent agreement can be observed between the SWCS and SCU methods in the whole blade height with errors of 2%~5%, and the calculation time of the SWCS method is only 2.5% of the SCU method, which is reduced from 7200 min to 180 min, making it possible to conduct the hot-to-cold analysis at the design stage.

Resonant response of turbomachinery blades can lead to high cycle fatigue (HCF) if the vibration amplitudes are significant. Therefore, the dangerousness assessment of the resonance crossing is important. It requires accurate predictions of the aerodynamic excitation, damping, and response, which will consume immense computational costs. The novel aspect of this study is the development of an efficient approach, which incorporates the time transformation (TT) method to predict the aerodynamic excitations and the harmonic forced response method to obtain the response levels. The efficiency and accuracy of this method were evaluated by comparing with traditional methods for the resonance crossing excited by upstream wake in a 1.5 multistage compressor. For the aerodynamic excitation, discrepancies of ±2% at the mean pressure and ±25% at the harmonic pressure in most areas expect for the blade root were observed, but the calculation time required by the TT method was only 5% of that by the time-marching method. Moreover, response levels with the same aerodynamic forces were compared between the harmonic forced-response and transient dynamic methods. Small differences in the displacement and stress variables were observed; the relative deviation was smaller than 2% with only 1% computing time compared with the transient method, indicating the high accuracy and efficiency of the efficient approach.

Blade tip timing (BTT) measurement has been used to measure the vibration of turbomachinery blades in recent years. People researches focus on the development of processing methods. Newly developed BTT processing methods are usually tested by numerical simulations. Because blades will deform when loaded, the detected points by sensors relative to the blade tip will deviate from their expected positions. A novel simulated BTT model is proposed to identify the movement of the detected points. Finite element method (FEM) is used, and the blade tip profile is discretized into series of segments, each of which is composed of adjacent nodes from the blade tip grid to avoid the error possibly caused by coarse girds. There are two factors which will deviate the detected points from their initial positions: static deformation and vibration. This method is validated by BTT datasets from three different simulations. In addition, an improved sine fitting method and a displacement modification method are proposed to process the deceptive signal of the detected point. The effect of the sensor configuration on the parameter identification is also studied. The result shows that when the static point cannot be determined, it would be better if the sensor could be mounted at a place where it is far away from the nodal line and the static deformation there is small.