Deterministic and Statistical Methods for Evaluating Turbine Rotor Speed Instabilities

This paper deals with the measurement and assessment of rotor speed instabilities. Mean attention is paid to measurements on turbine rotors while using the blade tip-timing method. The problematic was investigated on the model test turbine wheel of the Institute of Thermomechanics. A novel signal processing method, which consists of a combination of smoothing and approximation, is presented here. This procedure enables to define the instability function over a wide range of speeds and features more than one-order shorter calculation time compared with the fast Fourier transform. Moreover, the statistical approach was applied to test the time variability hypothesis of the studied processes, which was proved to be a very effective way for evaluating the nature of these processes.