Simulation studies on vibration control of compressor blades including foundation flexibility effects

Flutter and aerodynamically induced forced vibrations are common problems in the development of compressor blading for gas turbine engines. These types of flow induced vibrations can generate large stresses that lead to high cycle fatigue failures of the blades. To overcome this difficulty, the blades are redesigned to eliminate flutter, and to reduce the stress level of forced vibrations when the stress levels exceed design limits. During the blade redesign process, the blade shape is often altered in some fashion. These changes often decrease the performance of the compressor and may also increase engine weight. In order to maintain performance and weight goals, it is important to retain the optimal aerodynamic shape of the blades. To accomplish this goal, active/passive vibration control of flow-induced vibrations is being considered. Many investigators have studied the concept of actively controlling vibrations in plate-like structures, such as compressor rotor blades and stator vanes, through use of feedback control. One method involves mounting piezo-ceramic sheet to the surfaces on both sides of the plate surface. The piezo-ceramic sheet on one side of the plate is used as a sensor, and the sheet on the opposite side is used as an actuator. Sometimes, the structural model used in devising a control strategy assumes a boundary condition in which the plate is clamped at a rigid surface. In some applications, a rigid boundary condition assumption may not be realistic. The effectiveness of structural vibration control schemes often has a significant dependence on the accuracy of the structural model used in calculating control gains. In this paper, the concept of feedback control using piezo-ceramic sheets is applied to stator vanes of an axial flow compressor. An analysis method is outlined in which the structural model is developed using a commercial finite element code, ANSYS, which allows for easy implementation of a realistic model for practically any type of blade mounting condition, including mounting on a non-rigid surface. The model is exported to MATLAB, for calculation of control gains and simulation of the actively controlled system.