A Method for the Calculation of Friction Damping in Blade Root Joints

In turbomachinery, the complete detuning of turbine blades in order to avoid high cycle fatigue damage due to resonant vibration is often unfeasible due to the high modal density of bladed disks. To obtain reliable predictions of resonant stress levels of turbine blades, accurate modelling of friction damping is mandatory. One of the most common sources of friction damping in turbine blades is the blade root, where energy is dissipated by friction due to microslip between the blade and the disk contact surfaces held in contact by the centrifugal force acting on the blade. In this paper a method is presented to compute the friction forces occurring at blade root joints and to evaluate their effect on the blade dynamics. The method is based on an upgraded version of the state-of-the-art contact model, currently used for the non-linear dynamic analysis of turbine blades. The upgraded contact model is implemented in a numerical solver based on the harmonic balance method able to compute the steady-state dynamic response of turbine blades. The proposed method allows solving the static and the dynamic balance equations of the blade and of the disk, without any preliminary static analysis to compute the static loads acting at the contact interfaces.