Stall Flutter Simulation of a Transonic Axial Compressor Stage Using a Fully Coupled Fluid-Structure Interaction Jiaye Gan * , Hong-Sik Im † , Gecheng Zha ‡ Dept. of Mechanical and Aerospace Engineering University of Miami Coral Gables, FL 33124 gzha@miami.edu Abstract In this paper, numerical simulation of stall flutter for full annulus NASA Stage 35 is conducted using a fully coupled fluid/structure interaction. Time accurate compressible 3D Navier-Stokes equa- tions with Spalart-Allmaras turbulence model are solved with a system of 5 decoupled structural modal equations in a fully coupled manner. The 3rd order WENO scheme for the inviscid flux and 2nd order central difference for the viscous terms are used to accurately capture the interactions of the fluid and structure. Delayed detached eddy simulation is also applied to predict the flow induced vibration at near and stall conditions for comparison. The mechanism and aerodynamic damping behavior causing the stall flutter are analyzed. The effect of rotor stator interaction on the onset of flutter is studied. The fully coupled FSI simulation shows that Stage 35 has stall flutter at rotating stall. 1 Introduction Stall flutter is an aeromechanic instability that usually occurs at part-speed operation in turboma- chinery. It occurs when the energy absorbed by the blades from surrounding fluid exceeds the dissipating energy of the material and mechanical damping. The blade will vibrate exponentially and cause possible structure failure. Stall flutter could occur subsonic, transonic and supersonic incoming flow conditions. Transonic blades are widely used in modern fans/compressor, and are often prone to transonic stall flut- ter at off-design conditions. The flutter problem becomes more and more challenging with the modern light structures of compressor/fan such as blisk or integrated blade disks, which have little mechanical damping. Transonic flutter near stall conditions in turbomachinery are highly unsteady, non-linear and three di- mensional, which include flow induced vibration, flow separation, shock unsteadiness, shock wave/turbulent boundary interactions. The driving mechanism of the stall flutter in transonic turbomachinery may varied between the large separation and shock wave oscillation. Lepicovsky et al.[1] shows that the transonic stall flutter is triggered by the high frequency stall cell propagation in separated area on the airfoil suction side. There are no shock waves at high subsonic inlet Mach numbers (about 0.95) when transonic stall flutter occurred in their study[1]. Shwa et al.[2] demonstrates that the energy from shock wave oscillations is not strong enough to induce the transonic stall flutter based on a shock wave motion model. On the other hand, unsteady shock oscillation rather than blade stall was found to be the driving mechanism for flutter instability in a transonic fan[3]. The shock location and movement and its relation * Ph.D. † Ph.D., Currently an engineer at Honeywell ‡ Ph.D., Professor, Director of Aerodynamics and CFD Lab 1 Downloaded by Gecheng Zha on March 3, 2017 | http://arc.aiaa.org | DOI: 10.2514/6.2017-0783 55th AIAA Aerospace Sciences Meeting 9 - 13 January 2017, Grapevine, Texas AIAA 2017-0783 Copyright © 2017 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. AIAA SciTech Forum