A Parametric Study of a Cottage-Roof Damper and Comparison With Experimental Results

Abstract

Platform dampers are commonly used in turbomachinery to reduce the vibration amplitudes of the turbine blades. A blade-to-blade platform damper is simply a piece of metal which is pressed against two adjacent blade platforms by centrifugal force. Relative motions of the platforms lead to slip in the contacts and friction damping is provided in the system. The studied platform damper is designed with inclined contact surfaces. This type of damper is often called a cottage-roof damper or wedge damper. The inclination of the contact surfaces leads to variation of the normal load, which complicates the analysis of such dampers. In this paper, a simulation model is presented for a tuned bladed disk with cottage-roof dampers. This model includes normal load variation on the contact and a friction interface model valid for both macroslip and microslip. The elasticity of the damper body is often an important parameter for the performance of the damper and is included in the model. A comparison between solving the equation of motion in the frequency domain and the time domain is performed. It is found that the frequency domain solution with the fundamental frequency alone gives a result close to the time domain solution. The simulation model is validated with experimental data and it is found that the reduction of the resonance amplitude agrees well for the tested dampers. A parametric study is performed to find the optimal friction damper design. The studied parameters are the inclination of the contact surface, the coefficient of friction and the damper body stiffness. It is found that an increase in inclination of the contact surface and an increase in the coefficient of friction lead to a reduction of the optimal damper mass. An increase of the damper body stiffness results in a decrease of the resonance amplitude of the blade tip, particularly for high damper masses.