An Improved Blade Tip-timing Method for Vibration Measurement of Rotating Blades During Transient Operating Conditions

Abstract

Most of the traditional blade tip-timing (BTT) algorithms assume that the rotor speed within each revolution is constant, which is incorrect during transient operating conditions. To deal with the problem of speed transient, this paper puts forward an improved blade tip-timing method. A polynomial fitting using the once-per-revolution (OPR) sensor’s data was applied to approximate the speed change in one revolution. Then, a generalized sine-fitting (GSF) method was proposed to calculate the blade vibration information by utilizing the equivalent probe angle, which is related to the rotor speed. A new BTT simulator was built to study the effect of engine order (EO), amplitude and phase on the fitting results during linear acceleration and deceleration processes. Finally, an experiment was conducted to validate the proposed method during a linearly transient operating condition. In the numerical study, it is found that the fitting uncertainty of the GSF method is much lower than that of the traditional sine-fitting (TSF) method, especially for high engine order (EO > 1) cases. The experimental result confirms the feasibility of the new method during a linear run-up process with a relatively low-speed change rate (SCR), 0.11 Hz/rev approximately. Furthermore, it shows that the proposed method can eliminate the effect of speed change significantly, so that the calculated stack plot and blade amplitude are more reasonable.