Forced Response Analysis of Shrouded Blades by an Alternating Frequency/Time Domain Method

Abstract

In turbine jet engine, the rotating blades are subjected to cyclic loading, which makes the blades experience the so-called High Cycle Fatigue (HCF). Dry friction is often employed in turbine design to attenuate the blade vibration and increase aeroclastic stability of the turbine. The dry friction dampers are often classified into four types, i.e., blade-to-blade, blade-to-ground, shrouds, and wedge damper, respectively. Compared with the under-platform dampers, shrouds make fan behavior be significantly more complex. It is very difficult to model and predict the nonlinear response of shrouded blades. In the present study, an efficient approach to investigate the nonlinear response of the shrouded blades is suggested using an alternating frequency/time domain (AFT) method. On one hand, the friction force between shrouds is numerically solved in time-domain. The trajectory of relative motion of the moving contact point is traced, and the stick-slip-separation transition for 3-D relative motion of the shroud-contact interface is considered. On the other hand, the response of the shrouded blades is iteratively solved in frequency-domain using Harmonic Balance Method (HBM). In this approach, the influence of high frequency modes of blade, and the coupling of each harmonic component on damping behavior can be taken into account. As an application, the performance of shroud damper is systematically investigated using the AFT method. The influence of shroud-to-shroud preload and contact stiffness on the shroud damping potential is studied. Some valuable results are got to the design of the shroud contact.