Load-induced rotordynamic instabilities in turbomachinery

Abstract

By employing the extended Hamilton principle, both equations of motion and associated boundary conditions are derived for three different models subjected to non-conservative torques: the cantilevered rotor, the uniform shaft on rigid short bearings, and the uniform shaft on rigid long bearings. The characteristic frequency equations for these models are formulated by introducing a complex deflection and nondimensional parameters. Flexibility influence coefficients of the uniform shaft subjected to the tangential torque are found for the basis of linearized solutions. The conventional linear transfer matrix is modified to take into account the influence of load torque on the multidisk rotor-bearing system. By using a computer program, which is developed based on the modified transfer matrix, the effect of the tangential load torque on both the stability and the whirling frequencies is investigated for various models. The accuracy of numerical results obtained from the developed computer program is tested by considering simple models for which exact solutions are available. An experimental investigation on the torquewhirl effect (the nonsynchronous whirl caused only by load torque) is performed under controlled and measured conditions. The design concepts of the test rig, instrumentation, and test procedures are explained. Measurements are described which were made on the test rig to determine whirling amplitude, whirling frequency, torque, and speed for a number of combinations of load torque, damping, and rotor speed. The results of measurements are discussed and presented both in the time domain and in the frequency domain. A subsynchronous whirl frequency component was measured at the predicted torquewhirl frequency.