Blade tip timing and strain gauge correlation on compressor blades

Abstract

Traditionally, rotor blade vibration response measurements have been made using strain gauges. Rolls-Royce has a long experience of using strain gauge measurements to certify blades. In recent years, however, much effort has been invested in developing blade tip timing (BTT). The Rolls-Royce BTT system uses casing-mounted laser spot probes to measure the arrival times of the blade set. The vibration amplitudes of the blades are then inferred from these arrival times. BTT offers operational advantages over strain gauges and can measure every blade in the set. Previous back-to-back comparisons of strain gauges and tip timing have shown that both measurement systems measure the same trends in the data. However, initial analysis on a compressor rig showed that the two systems measured different response levels on the blades. This paper shows that both systems can be used with the finite-element model (FEM) to calculate the same amplitude-frequency level on the blade. This is provided that certain assumptions about the behaviour of the blades are true and that the uncertainties within both measurement systems are considered. The paper also presents a novel way of reporting the data to give a visual display of the quality of the data.

Blade resonance parameter identification based on tip-timing method without the once-per revolution sensor

“…Even though in reality damping is structural, experimental and theoretical study on single parameter method has proved that the approximation is feasible and the model is practical [5,8,9,11,12].…”

“…Compared to the traditional strain gauges based vibration measurement, the blade tip-timing method is a non-contact method and it can measure vibration parameters of all blades dynamically [4,5]. This method has become an industry-standard procedure for blade vibration measurement of turbomachinery and it is applied for damage prognosis of the turbine blades [6,7].…”

Interferometric Sensor System for Blade Vibration Measurements in Turbomachine Applications

“…The vibration parameter can be derived by evaluating the arrival times of the blades at the different sensors. Many sensor technologies have been explored for BTT systems, such as capacitive [5], eddy current [6], and optical principles [7], [8]. However, all electrical techniques are influenced by electromagnetic disturbances and do not perform at nonconducting materials, such as composite plastic materials that are in focus of rotor improvements [1].…”

“…Assuming f v t √ 12/π ≈ 1, the second summand in (7) is negligible in comparison to the first summand. This approximation is valid, since the signal duration t is about 1 s and the vibration frequency f v 1 Hz [7], [8]. Consequently, the limitation for the standard uncertainty of the vibration amplitude σ A x is the estimation of the velocity modulation amplitude A v and (7) simplifies to…”

Vibration sensing in smart machine rotors using internal MEMS accelerometers

“…Christensen and Santos [11] have used blademounted strain gauges as part of an experimental vibration control system. For qualification testing in the aerospace industry, Knappett and Garcia [12] provide an example of instrumentation of compressor blades with strain gauges to infer stress conditions. Sloetjes and de Boer [13] used strain gauges bonded to the surface of a rotor to measure bending of the shaft, although performance limitations were encountered.…”