Development of a coupled fluid/structure aeroelastic solver with applications to vortex breakdown-induced twin tail buffeting

Abstract

Simulation of tail buffet is studied for several delta wing-vertical
tail configurations. Flow conditions are chosen such that the wing
primary-vortex cores experience vortex breakdown and the resulting
turbulent wake flow impinges on the vertical tail. The dimensions and
material properties of the vertical tails are chosen such that the
deflections are large enough to insure interaction with the flow, and
the natural frequencies are high enough to facilitate a practical
computational solution. This multi-disciplinary problem is solved
sequentially for the fluid flow, the elastic deformations and the grid
displacements. The flow is simulated by time accurately solving the
laminar, unsteady, compressible, Navier-Stokes equations using an
implicit, upwind, flux-difference splitting, finite volume scheme. The
elastic vibrations of the tail are modeled by coupled bending and
torsion beam equations. These equations are solved accurately in time
using the Galerkin method and a five-stage, Runge-Kutta-Verner scheme.
The grid for the fluid dynamics calculations is continuously deformed
using interpolation functions to smoothly disperse the displacements
throughout the computational domain. Tail buffet problems are solved for
single tail cases, twin F/A-18 tail cases and twin highly swept generic
tail cases. The use of an apex flap for buffet control is also
computationally studied. The results demonstrate the effects of inertial
structural coupling, Reynolds number, aft fuselage geometry and spanwise
tail location on the tail buffet loads and response. Favorable
comparisons with experimental data indicate that the present aeroelastic
method is well suited to providing qualitative insight into the tail
buffet problem, as well as quantitative data for refined long duration
simulations.