An analytical forced response prediction system is used to predict turbomachinery airfoil vibratory stress amplitudes. The forced airfoil vibration can be caused by time dependent (unsteady) aerodynamic loads due to interaction with the flow field from neighboring airfoils rows, such as shocks, wakes, or pressure waves, or due to self induced unsteady aerodynamics such as vortex shedding and unsteady tip vortices. The amplitude of the forced response is of particular interest when the frequency of the time dependent unsteadiness is close to the natural frequency of the forced airfoil. At this condition, the airfoil is at or near resonance and vibratory stress can exceed the material capability causing high cycle fatigue (HCF) failures.
The airfoil forced response prediction system presented here combines structural static and dynamic analysis with steady and unsteady computational fluid dynamic analysis in an iterative coupled solution to the aeroelastic problem. The system includes three dimensional viscous multistage steady and unsteady computational fluid dynamics and three dimensional geometric nonlinear structural static, linear free vibration and modal forced response analysis to predict the airfoil amplitude in the resonance modes during engine operation.
This analysis system is being used to help identify the cause of HCF failure and determine corrective action. The analysis system is demonstrated using a compressor rotor excited by upstream and downstream vanes. Results are then compared with engine test data.