This paper study the non-synchronous vibration (NSV) of a high speed multistage axial compressor using rigid blade and vibrating blade with fluid-structural interaction (FSI). The unsteady Reynolds-averaged Navier-Stokes (URANS) equations and mode based structural dynamic equations are solved. A low diffusion E-CUSP Reimann solver with a 3rd order WENO scheme for the inviscid fluxes and a 2nd order central differencing for the viscous terms are employed. A 1/7th annulus sector of IGV-rotor-stator is used with a time shifted phase lag BC at circumferential boundaries. An interpolation sliding boundary condition is used for the rotor-stator interaction. The URANS simulation for rigid blades shows that the leading edge (LE) tornado vortices, roughly above 80% rotor span, travel backwards relative to the rotor rotation and cause an excitation with the frequency agreeing with the measured NSV frequency. The predicted excitation frequency of the traveling vortices in the rigid blade simulation is a non-engine order frequency of 2603 Hz, which agrees very well with the NSV rig testing. For the FSI simulation, the results show that there exist two dominant frequencies in the spectrum of the blade vibration. The lower dominant frequency is close to the first bending mode. The higher dominant frequency close to the first torsional mode agrees very well with the measured NSV frequency. The simulation conducted in this paper appears to indicate that the NSV is excited by the traveling vortex.
This paper examines the lock-in hypothesis of non-synchronous vibration (NSV) in a high speed multistage axial compressor. The unsteady Reynolds-averaged Navier-Stokes (URANS) equations and modal approach based structural dynamic equations are solved. A low diffusion E-CUSP approximate Riemann solver with a 3rd order WENO scheme for the inviscid fluxes and a 2nd order central differencing for the viscous terms are employed. The structural vibration of the blades are solved by a set of modal equations that are fully coupled with the flow equation. The rigid blade simulations are conducted to examine the main driver of NSV. A 1/7th annulus sector of IGV-rotor-stator is used with a time shifted phase lag BC at circumferential boundaries. A dominant excitation frequency caused by the traveling tip vortices are captured. The excitation frequency is not on the engine order. The simulation is then switched to fluid structure interaction that allows the blades to vibrate freely under the flow excitations. The matching of aerodynamic forcing frequency with the structure response frequency seems indicating that the NSV of this compressor is a limit cycle oscillation (LCO) excited by aerodynamic forcing, not caused by flow frequency/phase locked to structural frequency. The rotating speed is varied within a RPM range, in which the rig test detected the NSV. The unsteady flows with rigid blades are simulated first at several RPMs. The simulation indicates that the structure response follows the frequency of the flow excitations existing in the rigid blades. At least under the simulated conditions, the NSV does not appear to be a lock-in phenomenon, which has the flow frequency lock-in to the structure natural frequency.
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