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

Abstract

A high speed 1-1/2 axial compressor stage is simulated in this paper using an Unsteady Reynolds-Averaged Navier-Stokes (URANS) solver for a full-annulus configuration to capture its non-synchronous vibration (NSV) flow excitation. The simulation presented in this paper assumes rigid blades. 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 blades and fluid flow. A fully conservative rotor/stator sliding boundary condition is employed with multiple-processor capability for rotor/stator interface information exchange for parallel computing. The sliding BC accurately captures unsteady wake propagation between the rotor and stator blades while conserving fluxes across the rotor/stator interfaces. The predicted dominant frequencies using the blade tip response signals are not harmonic to the engine order, which is the NSV excitation. The simulation is based on a rotor blade with a 1.1% tip-chord clearance. Comparison to previous 1/7th annulus simulations show previous time-shifted phase-lag BCs are accurate. The NSV excitation frequency of the full annulus simulation is for the most part 3.3% lower than experimental and matches with the 1/7th annulus simulation, although some blades displayed slightly different NSV excitation frequencies. The full annulus simulation confirms that 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 excitation. This instability is present in all blades of the rotor annulus. While the time-shifted phase lag BCs can accurately capture the frequency of NSV excitation, phenomena related to flow separation with lower frequencies, including dual-vortex systems within blade passages, are not captured by the 1/7th annulus simulation, but are found in the full-annulus simulation. Nomenclature e total energy per unit mass L ∞ blade chord at hub N B number of blade N D number of nodal diameter p static pressure R o Rossby number, ΩL ∞ U ∞ r radius T period for one nodal diameter * Ph.D. Student † Ph.D., Currently an engineer at Honeywell ‡ Professor.

Investigation on the Mechanism and Parametric Description of Non-Synchronous Blade Vibration

“…The blade vibration is attributed to the oscillating blade tip vortex by Hwang et al [ 13 ]. By using the model of Kielb [ 14 ], studies have been carried out by Zha et al [ 15 , 16 , 17 , 18 , 19 , 20 ] to explore the flow at tips. The results reveal that the tip clearance shape has an influence on the frequency of NSV [ 15 ].…”

“…The results reveal that the tip clearance shape has an influence on the frequency of NSV [ 15 ]. The separation vortex of the tornado structure in the flow field and the tip leakage flow are the main factors of the blade non-synchronous vibration [ 17 ]. This kind of vortex travels on the suction side in the passage, crossing to the leading edge of the next blade in the counter rotating direction.…”

Investigation on the Flow Field Entropy Structure of Non-Synchronous Blade Vibration in an Axial Turbocompressor

“…Zha et al [ 14 , 15 , 16 , 17 , 18 , 19 ] carried out a series of works with the same compressor of Kielb [ 2 ], established 1/7th and full annulus models for the 1.5-stage compressor. The RANS simulations [ 14 ] show that the tip clearance shape has a strong influence on the frequency of NSV.…”