Identification of modal parameters and aeroelastic coefficients in bladed disk assemblies

Abstract

Unknown excitation forces are applied to bladed disk assemblies leading to forced vibration responses and non-contact measurement of such vibrations are obtained using blade tip-timing signals. In the tip-timing data analysis, a set of optical probes is mounted on an engine casing and measures the times of arrival of each blade. These timings are then used to estimate the vibrations of different blades and current research focuses on analysis methods for interpretation of the measured vibration data from the limited number of probes. We present in this paper a methodology to identify the modal properties of mistuned bladed disk from tip-time data. The tip-timing measurements are under-sampled and we propose a technique to obtain a continuous signal. The subspace algorithm is then applied to the reconstituted signal for modal parameter identification. A technique to identify aeroelastic coefficients from output data only is also proposed. The main difficulties that we have to overcome are the unknown excitation forces, the very high modal density (77 eigenfrequencies in a narrow band of 1 Hz) and the signal reconstitution from under-sampled data. Numerical and experimental results are presented.