Numerical Simulation of Aerodynamic Damping for Flutter Analysis of Turbomachinery Blade Rows

This paper describes the calculation of aerodynamic damping for prediction of flutter characteristics of turbomachinery blade rows. The unsteady aerodynamic blade loads are obtained by solving the Navier-Stokes equations on a dynamically deforming, body-fitted grid. Phase-lagged boundary conditions are used to model the nonzero interblade phase angle oscillations, and the energy exchange method is used to calculate the aerodynamic damping. The analysis is applied to calculate flutter of a transonic forward-swept fan configuration, which showed flutter at part speed conditions in wind-tunnel tests. The analysis successfully identified the most critical mode and the flow characteristics responsible for the observed flutter. The location of shock wave and variation of its strength were found to strongly influence the aerodynamic damping, with outboard stations providing the main contribution. The results also demonstrate that changes in blade shape impact the calculated aerodynamic damping, indicating the importance of using an accurate blade operating shape under centrifugal and steady aerodynamic loading. Sensitivity of the calculated aerodynamic damping to variation in inlet and exit conditions, the computational time steps, and blade natural frequency are also reported. (Author)