A Methodology to Predicting Total Damping of Axial Compressor Shrouded Stator Vanes

Abstract

The main objective of this paper is to evaluate the capability of existing numerical tools to predict the total damping Q values of axial core compressor shrouded stator vanes with a view to use them in the forced response simulations. Here, the aerodynamic damping is calculated for a wide range of vane vibration modes and nodal diameters (inter-blade-phase angles) using a CFD based aeroelasticity program. The mechanical friction damping of vane vibration modes is computed by using a multi-harmonic balance forced response code. These calculations take into account the effects of normal contact forces, friction coefficients, contact stiffness and excitation (forcing) loads. A pragmatic methodology has been developed to calculate the aerodynamic and mechanical friction damping values and hence predicting total Q values of stator vanes. Sensitivity studies are performed to assess the effects of mass flow and inter-blade-phase angles on aerodynamic damping. Moreover, the analyses allowed to identify the modeshapes associated with either high aerodynamic or mechanical damping or both. The numerical results are correlated with experimentally measured total Q values from strain gauge engine tests. This work shows that the current numerical tools have the capability to predict not only the aerodynamic forcing but also aerodynamic and mechanical friction damping values. Therefore, the analysis tools and methodologies close the stator vane forced response prediction capability loop. It means the vane force responses can be predicted as measured from strain gauge engine tests. This constitutes an important step in the development of axial compressors test-to-simulations, as more efforts are being placed towards the development of whole engines test-to-simulations.