Abstract
Rotating blade is one of the most important components for turbomachinery. Blade crack is one of the most common and dangerous failure modes for rotating blade. Therefore, the fault mechanism and feature extraction of blade crack are vital for the safety assurance of turbomachinery. This study is aimed at the nonlinear dynamic model of rotating blade with transverse crack and the prior feature extraction of blade crack faults based on the vibration responses. First and foremost, a high-fidelity breathing crack model (HFBCM) for rotating blade is proposed on the basis of criterion for stress states at crack section. Since HFBCM is physically deduced from the perspective of energy dissipation and the coupling between centrifugal stress and bending stress is considered, the physical interpretability and the accuracy of the crack model are enhanced comparing with conventional models. The validity of the proposed HFBCM is verified through the comparison study among HFBCM, conventional crack models, and finite element-based contact crack model (FECCM). It is suggested that HFBCM behaves best among the analytical models and matches well with FECCM. With the proposed HFBCM, the nonlinear vibration responses are investigated, and four types of blade crack detection indicators for rotating blade and their quantification method are presented. The numerical study manifests that all these indicators can well characterize the occurrence and severity of crack faults for rotating blade. It is indicated that these indicators can serve as the crack-monitoring indexes.
Highlights
Rotating blades, one of the core components of rotating machines, are extensively applied in modern industry such as gas turbines, jet engines, power plants, pumps, helicopters, and wind turbines
Despite the advances in theory and technology of blade fault diagnosis over many years, effective and accurate measurement of blade vibration performance still encounters with some significant challenges, which in turn triggers the need for further improvements on the comprehending of blade vibration phenomenon.[6]
It is worth noting that all these indexes including Nonlinear damage indicator (NDI), phase diagram indicator, time-frequency indicator, and disturbance indicator present a monotonous variation tendency with the increasing crack depth, which indicates that they can serve as the condition indexes for blade crack monitoring
Summary
One of the core components of rotating machines, are extensively applied in modern industry such as gas turbines, jet engines, power plants, pumps, helicopters, and wind turbines. According to the comparative results presented, the following conclusions can be drawn: (i) the proposed HFBCM behaves best among all the models under the illustrated four conditions; (ii) under stationary Condition I, the three models (HFBCM, SBCM, and BBCM) have the same accuracy for the vibration prediction since there is no centrifugal effect; (iii) under rotational Condition II, since conventional crack models (BBCM, CBCM, and OCM) cannot capture the vibration characteristics induced by additional bending moment, there are large errors showed up, which can be observed in Figure 8(b) and (c); (iv) under rotational Conditions III and IV, the breathing behavior of blade crack is predominant by the bending stress since the excitation load is large enough compared with the centrifugal force. This result indicates that the natural frequency shift may serve as the presence of severe crack and, to some degree, indicates the tendency of crack depth, that is, the severity
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