Rotating blade frequency identification by single-probe blade tip timing. (1st June 2022) - Cao, Jia-Hui
Abstract: The rotating blade is a key turbomachinery component with a high failure risk. Therefore, monitoring the rotating blade is urgently required. Blade tip timing (BTT) is regarded as an efficient technique for blade vibration monitoring as it reflects the condition of blades. However, the identification process from under-sampled data and probe layout optimization hinder the application of BTT. Most of the existing parameter identification methods have strict probe layout requirements; thus, an inappropriate probe layout may fail BTT measurements. An increased number of probes and optimal probe positions are considered essential for frequency identification. However, an optimal probe layout is usually restricted by arrangement. In this work, a novel frequency identification method via a single BTT probe is proposed by considering arrangement, cost, and safety restrictions. The proposed method focuses on the relationship between sampling and aliasing frequencies, which can be summarized in two steps: obtaining a Sampling–Aliasing Frequency (SAFE) map and identifying the resonance center and corresponding engine order (EO). Obtaining the SAFE map of the BTT signal recorded by a single probe is difficult because of low and variable sampling frequency. To overcome this problem, the adaptive window length short-time Fourier transform is proposed. Based on the SAFE and EO, the natural frequency can be accurately extracted from a single BTT measurement. Uniformly and nonuniformly variable speed conditions were investigated, and the results were compared with those obtained using multiple probes. The proposed method has been verified to provide blade natural frequency from a single-probe BTT measurement. Highlights: Natural frequencies of blades are accurately estimated by a single probe. Sampling frequency is used for undersampling signal analysis. An adaptive window length short time Fourier transform is proposed for BTT. SAFE map is constructed to extract natural frequency and engine order. The proposed method is suitable for both uniformly and nonuniformly variable speed cases.