Rotating Structure Modeling and Damping Measurements

The structural damping is of importance to suppress the vibration amplitude of compressor blades rotating at high angular velocity under a high cycle impact. To avoid the appearance of the high cycle fatigue (HCF), damping materials may be applied to the compressor blades. To quantify the effect while using damping materials, a numerical tool needs to be developed for the damping prediction of a dynamic rotating blade. This thesis is divided into two parts: Paper A develops a dynamic model of a rotating blade and Paper B a damping structure model including measurements. In Paper A, a dynamic rotating blade model is developed by using a plate model at an arbitrary stagger angle. Hamilton’s principle is applied to derive a system of equations of motion and the corresponding boundary conditions. Numerical simulation is implemented to perform eigenfrequency analysis by the Extended Galerkin method. In addition, parametric analysis is performed with respect to rotation speed and stagger angle, respectively. Results show a good agreement with those of the finite element method. Finally, forced response analysis is determined for two cases; a point force and a distribution force, using a proportional damping model. In Paper B, unconstrained and constrained damping techniques are applied to increase the structural damping of the blades, including measurement and modeling results. Two specimens, titanium and stainless steel, are treated by aluminum oxide and epoxy coating material. Measurement results show that both treatments give damping increase, where aluminum oxide is more effective for damping improvement than the corresponding epoxy treatment. The unconstrained damping layer model is used to predict the total material damping of the combined structure as well as the material damping of coating layer. Furthermore, the constrained-layer model is used to optimize the damping configuration. Two compressor blades in titanium and stainless steel are tested in air and vacuum. One reason is being that the radiation loss factor increases the total damping comparing with that under vacuum condition. The calculation of radiation loss factor is performed to match the measurement data. Finally, increased material damping decreases peak stress and therefore increases the life time of the compressor blades.QC 20110311