Simulation of Non-Synchronous Blade Vibration of an Axial Compressor Using a Fully Coupled Fluid/Structure Interaction

Abstract

In this paper non-synchronous vibration (NSV) of a GE axial compressor is simulated using a fully coupled fluid/strcuture interaction (FSI). Time accurate Navier-Stokes equations are solved with a system of 5 decoupled structure modal equations in a fully coupled manner. A 3rd order WENO scheme for the inviscid flux and a 2nd order central differencing for the viscous terms are used to resolve nonlinear interaction between vibrating blades and fluid flow. 1/7th annulus is used with a time shifted phase-lag (TSPL) boundary condition to reduce computational efforts. A fully conservative rotor/stator sliding boundary condition is employed to accurately capture unsteady wake propagation between the rotor and stator blades. The predicted dominant frequencies using the blade tip response signals are not harmonic to the engine order, which is the NSV. The blade vibration is torsionally coupled with highly oscillating blade pressure and is not damped out during the NSV. No resonance to the blade natural frequencies is found. The instability of tornado vortices in the vicinity of the rotor tip due to the strong interaction of incoming flow, tip vortex and tip leakage flow is the main cause of the NSV observed in this study.

Investigation of Non-synchronous Vibration Mechanism for a High Speed Axial Compressor Using Delayed DES

“…These two low pressure regions create a pair of coupling forces that generates a torsion moment causing NSV. This is consistent with the experimental and numerical observations in [4,18] that the NSV of this rotor is dominant at its first torsion mode(2nd mode). The frequency of this tornado vortex propagation captured is roughly equal to the NSV frequency of the blade pressure signals.…”

“…In addition, an efficient time-shifted phaselagged BC [18] with nodal diameter of 5 is applied at the lower/upper circumferential boundaries to facilitate 1/7th annulus simulations.…”

Full-Annulus Simulation of Non-Synchronous Blade Vibration of an Axial Compressor

“…These two low pressure regions create a pair of coupling forces that generates a torsion moment causing NSV. This is consistent with the experimental and numerical observations in [2,27] that the NSV of this rotor is dominant at its first torsion mode(2nd mode). The frequency of this tornado vortex propagation captured is roughly equal to the NSV frequency of the blade pressure signals.…”

“…This near-blade-tip RI has been shown to occur in all rotor blades of the 1/7th annulus simulations [10,27], and the present simulation shows that this instability is also present in all the blades of the full-annulus simulation as shown in Fig. 8.…”

“…Previous unsteady simulations of the present high-speed compressor [2,10,27] have shown that a rotating instability (RI) above 78% of the span causes NSV. This near-blade-tip RI has been shown to occur in all rotor blades of the 1/7th annulus simulations [10,27], and the present simulation shows that this instability is also present in all the blades of the full-annulus simulation as shown in Fig.…”