A blade tip-timing method without once-per-revolution sensor for blade vibration measurement in gas turbine engines

Abstract

The blade vibration measurement is crucial for gas turbine engines to ensure safe operations. One of the techniques is blade tip-timing (BTT), which is under the assumption that rotor speed is constant and depends on a once-per-revolution (OPR) timing reference to calculate the blade tip displacement and to identify the blade sequence. However, this assumption is incorrect for transient conditions, and the installation of an OPR sensor sometimes is not allowable and reliable. These reasons greatly limit the application of the BTT technique. This paper proposes a self-correcting (SC)-BTT method to realize the blade vibration measurement under different operating conditions without the use of an OPR sensor. The proposed method is based on polynomial fitting, and a reference probe is used to correct high-order fitting coefficients. Numerical results show that the SC-BTT method can greatly reduce the fitting error caused by blade pitch and vibrational parameters. Experimental results demonstrate that the proposed method is capable of removing the limitation of the lack of an OPR sensor and overcoming the drawbacks of the OPR system, such as the failure of the OPR sensor or low-speed resolution. For three investigated cases, the relative errors of derived rotor speed are below 0.12%. The relative error of blade peak-to-peak amplitude (PPA) and initial phase angle are around 3% at the resonance region with engine order (EO) 2.