Investigation of Flow Instability Mechanism Causing Compressor Rotor-Blade Nonsynchronous Vibration

Abstract

This paper investigates the aerodynamic excitation mechanism of the rotor-tip flow instabilities leading to nonsynchronous vibration in a high-speed multistage axial compressor. Numerical simulations for the one-seventh annulus periodic sector of 1-1/2 stage are performed using an unsteady Reynolds-averaged Navier–Stokes solver with a fully conservative, sliding interface, boundary condition to capture wake propagation between adjacent blade rows. The present numerical simulations for rigid blades demonstrate that the tip flow instability is the main cause of the compressor nonsynchronous vibration excitation and is generated by the circumferentially traveling vortices. The frequency of the vortex passing each blade in the counter-rotation direction is roughly equal to the nonsynchronous vibration excitation frequency. Three different rotor-tip clearance sizes and shapes are studied. The nonsynchronous vibration excitation frequency and amplitude vary slightly with the tip clearance size when the clearances have the same flat shape, but they change substantially when the tip clearance has a convex-type shape. The predicted nonsynchronous vibration excitation frequency is in excellent agreement with the rig testing.