Viscosity Influence on Flutter Boundary and Limit Cycle Oscillation in Transonic Regime

Abstract

Viscosity has a great influence on nonlinearity especially in the transonic regime: however only preliminary research into the viscous effect on the aeroelstic response was conducted. Nonlinearity of the flowfield assumed to be the main source of flutter behaviours. This paper reports the results of intensive numerical simulations carried out on 2D aerofoil sections to investigate the effect of viscosity on flutter boundary and especially on limit cycle oscillation (LCO) characteristics. Unsteady Euler and Navier-Stokes flow solvers are developed for use in aeroelastic analysis with the moving grid method, while the aeroelastic response is calculated with the aeroelastic equations of motion in two degrees of freedom. The flow solvers are verified with simulations of pitching aerofoil. Two aeroelastic test cases ranging from subsonic to transonic flow regimes (M∞=0.3∼0.92, Rec = 12.3×106) were simulated in depth to obtain flutter boundaries as well as characteristics of LCO. The results indicate that the LCO occurs in the subsonic flow regime as well as in the transonic flow regime with far greater intensity caused by viscous effect. It has been shown that the weak divergence is found to be a transonic aeroelastic phenomenon.