Fluid/Structural Dynamic Interaction

Description of the Problem

On a fighter aircraft operating at high angles of attack (e.g., F/A-18), vortices emanating from the leading-edge extension of a delta wing breakdown before reaching the vertical tails, which get bathed in a wake of unsteady highly-turbulent, swirling flow. The vortex-breakdown flow produces unsteady, unbalanced loads on the vertical tails which in turn produce severe buffet on the tails and has led to their premature fatigue failure. Computational simulation of a full fighter aircraft is economically impractical. The objective of this work is to simulate and predict the buffet response of the F/A-18 aircraft by isolating the ingredients of the buffet from the whole aircraft using delta wing-swept back vertical tail configuration in transonic vortex-breakdown flow.

Flow Conditions and Configuration

• 65-degree cropped delta wing.
• A 35 degree swept-back vertical tail of aspect ratio 1.4, taper ratio is 0.39.
• Navier-Stokes Equations are used for the fluid dynamics and aeroelastic equations are used for the structural dynamics.
• Mach number is 0.85, angle of attack is 28 degree, Reynolds number is 3.23 million, and the flow is assumed to be laminar.
• A O-H grid of 65 X 43 X 95 in the wrap-around, normal and axial directions, respectively is used.

Movie (1332026 bytes, 41 frames).

Three-dimensional view of the wing-tail configuration shows the constant total-pressure surfaces. The color is the static pressure contours.

Acknowledgement

This work is supported under Grants No. NAG-1-648 and NAG-1-994 by the NASA Langley Research Center. The computational resources provided by the NAS facilities at Ames Research Center and the NASA Langley Research Center are appreciated and recognized.

Thanks are also extended to the research team:

• Prof. Osama A. Kandil
• Mr. Steven J. Massey
• Mr. Essam F. Sheta

for their contribution to this page.