Modelling and simulation of blade tip timing uncertainty from rotational speed fluctuation

Abstract

Blade Tip Timing (BTT) is considered a promising technique for characterizing blade vibration in which non-contact timing sensors are used to measure the arrival time of the blade passing each sensor. For vibration features extraction from BTT measurement, rotational speed is a key factor. In current researches, the vibration parameters are usually identified on the assumption of steady rotational speed or constant rotary acceleration. Practically, complex conditions in rotating machinery such as airflow instability result in rotational speed fluctuation inevitably, which may lower the accuracy of vibration parameters identification. In this paper, the BTT uncertainty from rotational speed fluctuation is analyzed theoretically and demonstrated via simulation. Firstly, a simulated BTT system which consists of a rotational blade, exciting forces and BTT sensors is set up. Two types of speed fluctuation, i.e. normally distributed and uniformly distributed random fluctuation are considered in this system. The arrival time of the blade at any sensor and its vibration displacement are acquired by simulation. Then, the vibration parameters of the blade are identified using a widely-used approach in BTT measurement. From the results, the BTT uncertainty from speed fluctuation is discussed and summarized, which lays the foundation for uncertainty elimination of BTT measurement in further work.