Non-Contact Measurement of Blade Vibration in an Axial Compressor

Abstract

Complex blade responses such as a rotating stall or simultaneous resonances are common in modern engines and their observation can be a challenge even for state-of-the-art tip-timing systems and trained operators. This paper analyses forced vibrations of axial compressor blades, measured during the bench tests of the SO-3 turbojet. In relation to earlier studies conducted in Poland with a small number of sensors, a multichannel tip-timing system let us observe simultaneous responses or higher-order modes. To find possible symptoms of a failure, blade responses in a healthy and unhealthy engine configuration with an inlet blocker were studied. The used analysis methods covered all-blade spectrum and the circumferential fitting of blade deflections to the harmonic oscillator model. The Pearson coefficient of correlation between the measured and predicted tip deflection is calculated to evaluate fitting results. It helps to avoid common operator mistakes and misinterpreting the results. The proposed modal solver can track the vibration frequency and adjust the engine order on the fly. That way, synchronous and asynchronous vibrations are observed and analysed together with an extended variant of least squares. This approach saves a lot of work related to configuring the conventional tip-timing solver.

Sensing Applications in Aircrafts Using Polymer Optical Fibres

“…Whereas the BTT measurement provides useful information for SHM, the TC measurement relates to engine efficiency. On the one hand, most BTT solutions used by industry employ several sensors mounted circumferentially and they are still based on algorithms established at the end of the 20th century, even though several alternatives are currently being explored (more details can be found in [ 36 ]). On the other hand, there are several TC measurement systems that use different technologies, such as capacitive, eddy current, pneumatic, strain gauges, electromechanical, microwave, and optical sensors (see the introduction in [ 37 ] for additional details).…”

Analysis of Fan Blade Vibration with a Non-Contact Method

“…To process TOA data from several sensors, Least Squares fitting is used, which is described in detail in [7,8,17,18]. Its main assumption is that the tip displacement of each blade is modelled as a sine wave for every revolution.…”

“…The positions of probes around the casing/frame are crucial to analyse BTT data. The idea was to exploit a sine fitting algorithm [17] to extract the frequency and amplitude data, so it was possible to choose a non-uniform spacing between the probes. This choice was made, because, in case of a uniform spacing, the system is 'blind' to some engine orders.…”

Advanced Materials and Technologies for Compressor Blades of Small Turbofan Engines

“…This makes it possible to ensure not only a high level of their strength reliability (safety factor), but also a decrease in the mass of parts. It is known that reducing the mass of the rotor of a gas turbine engine is one of the important directions for improving the design, since it effectively reduces the level of dynamic loads and vibration [49]. However, taking into account that the analysed technologies for obtaining ingots for compressor components (powder metallurgy and severe plastic deformation) lead to a change in the indicated characteristics of materials at the level of 10%, they were not considered as a criterion for choosing a production technology.…”