Biprobes polynomial fitting method to calculate synchronous vibration displacement based on OPR-free blade tip timing

Aero-engine blades operate under harsh conditions and are prone to cracks, necessitating robust health monitoring solutions. Blade Tip Timing (BTT) a non-contact vibration measurement technology, enables simultaneous monitoring of all blades. However, traditional BTT methods heavily rely on Once-Per-Revolution (OPR) sensors to track rotational timing. If the OPR signal is inaccurate, the entire testing system fails to function. It is necessary to study OPR-free methods. The existing methods usually need to install more than four sensors to recover the blade vibration signal accurately. To reduce the number of sensors required, we propose the Biprobes Polynomial Fitting the BTT (BPF-BTT) method which is a novel two-sensor framework that achieves high-precision synchronous vibration measurements through optimized sensor placement and polynomial fitting algorithms. The experimental results show that the displacement error of BPF-BTT is only 0.027 mm under synchronous resonance condition, which is half of the error of the existing method. The BPF-BTT method has excellent results in practical application.