Effect of Static/Dynamic Coupling on the Forced Response of Turbine Bladed Disks With Underplatform Dampers

Abstract

Friction contacts are often used in turbomachinery design as passive damping systems. In particular underplatform dampers are mechanical devices used to decrease the vibration amplitudes of bladed disks. Numerical codes are used to optimize during design the underplatform damper parameters in order to limit the resonant stress level of the blades. In such codes the contact model plays the most relevant role in the calculation of the dissipated energy at friction interfaces. One of the most important contact parameters is the static normal load acting at the contact, since its value strongly affects the area of the hysteresis loop of the tangential force and therefore the amount of dissipation. A common procedure to estimate the static normal loads acting on underplatform dampers consists in decoupling the static and the dynamic balance of the damper. A preliminary static analysis of the contact is performed in order to get the static contact/gap status to use in the calculation, assuming that it does not change when vibration occurs. In this paper a novel approach is proposed. The static and the dynamic displacements of the system (bladed disk + underplatform dampers) are coupled together during the forced response calculation. Static loads acting at the contacts follow from static displacements and no preliminary static analysis of the system is necessary. The proposed method is applied to a numerical test case representing a simplified bladed disk with underplatform dampers. Results are compared with those obtained with the classical approach.