Mechanism of aerodynamic excitation due to wake

potential and shock wave interaction was studied by numerical simulation of unsteady flows in a high pressure turbine stage.The excitation source was identified by analyzing a space-time map and distortion tracing technique.The excitation source was identified as the upstream blade-passing frequency by analysis of unsteady pressure on the blade surface.The unsteady excitation strength was quantified by normalized unsteady disturbances.Several configurations with different axial spacings were calculated.The results indicate that with small changes in axial spacing while maintaining same time-average aerodynamic characteristics

the aerodynamic excitation increases while reducing axial gap and the aerodynamic excitation may excite the blade vibration in a torsion mode.