Aeroelastic Instability Evaluation of Transonic Compressor at Design and off-Design Conditions

Abstract

Aeroelastic flutter investigation of a three-stage transonic axial compressor rotor is discussed in this paper. Unsteady CFD analyses were used to evaluate the flutter instability of the test compressor. Investigation on the effect of inlet guide vane and blade stiffness on aeroelastic damping is the prime objective of this study. The blade was subjected to vibration in CFD domain at specified frequency and amplitude. The unsteady aerodynamic force and work done by the blade at each vibration cycle were evaluated using fluid structure interaction technique. Energy method and work per cycle approach were adapted for this flutter prediction. Based on the work per cycle value, aerodynamic damping ratio was evaluated. A computational framework has been developed to calculate work per cycle and thereby aerodynamic damping ratio. Based on the magnitude and sign of aerodynamic damping ratio, occurrence of flutter was evaluated at all operating conditions of the engine. The primary cause for blade flutter was identified as large flow separation and flow unsteadiness due to high incidence on blade suction surface. The flow unsteadiness resulted into aerodynamic load fluctuation which matched with blade natural frequency and further resulted in blade excitation. Flutter boundary was evaluated for both with and without inlet guide vane case. Significant improvement in flow pattern and flutter boundary was observed for the case with inlet guide vanes.