Computation of Nonlinear Viscous Panel Flutter Using a Fully-Implicit Aeroelastic Solver

The implicit time-accurate approach developed by Morton, Melville and Visbal (1997) is extended to account for structural nonlinearities in fluid-structu re interactions. The flow equations are solved employing the Beam-Warming, alternate-direction, implicit scheme. The structural dynamic equations are solved by the Newmark-/3 method in time and a finite-differe nce method in space. Particular attention is focused on the elimination of the lagging errors associated with the exchange of loads and deformations at the fluid-structure interface. The implementation of Newton-like subiterations allows the coupling of vastly different aerodynamic and structural integration schemes while providing enhanced numerical stability and temporal accuracy relative to traditional lagged approaches. The nonlinear flutter of a panel is chosen as a model problem in order to address relevant issues of the fluid-structure interaction methodology. The phenomenon is modeled by coupling either Euler or Navier-Stokes equations for the fluid with the nonlinear plate deformation equations. The stability boundary of a simply-supported panel is computed for both inviscid and laminar viscous flow in the transonic regime. The approach is validated by spatial and temporal resolution studies, as well as by comparison with previous computational results. Comparison of Euler and laminar Navier-Stokes solutions reveal a pronounced stabilization of the panel due to viscous effects near sonic Mach numbers.