An experimentally validated modal model simulator for the assessment of different Blade Tip Timing algorithms. (February 2020) - Mohamed, Mohamed Elsayed
Highlights: A novel BTT data simulator based on modal data of a blisk's FE model is presented. Modal coordinates enables efficient generation of BTT data for complex geometries. The simulator can efficiently and accurately capture dynamic effects. It can also allow the study of the effect on BTT methods of various types of error. The simulator is applied to experimentally validated FE model to generate BTT data. The simulated BTT data used for an assessment of three principal BTT methods. The assessment focuses on performance and limitations for different conditions. The BTT methods and data preparation are presented in detail. Effect of data preparation on all methods is investigated for the first time. Abstract: Blade Tip Timing (BTT) technology is concerned with the estimation of turbomachinery blade vibration. A BTT system comprises two parts: (a) measurement system for blade tip arrival times ("BTT data"); (b) the analysis algorithms. Simulators that generate BTT data play a key role in BTT development since they enable an assessment of the performance of the different BTT algorithms. Such assessments are not feasible with real engine data since they require controlled conditions and knowledge of the true tip vibration as the reference. Most simulators in the literature are based on a simple spring-mass-damper model and commercially available ones have no physical underpinning. This work presents a novel realistic simulator based on the experimentally validated Finite Element (FE) model of a bladed disk (blisk). Transformation to modal space enables the efficient generation of simulated BTT data regardless of the complexity of the blisk geometry. The simulator is then used in a first-time comparative study of three principal BTT algorithm methods (autoregressive, sine fitting, two-parameter plot) under various conditions involving synchronous and asynchronous excitations with both single and simultaneous frequencies. The study clarifies obscurities in the methods and demonstrates the applicability of each method to different BTT system scenarios.