VISCOUS-FLOW SIMULATION OF A FIGHTER AIRCRAFT

Abstract

A computer code capable of solving the three-dimensional compressible, unsteady, Navier-Stokes equations has been developed. This solver has been applied to steady and unsteady subsonic flow past highly swept wings and wing-body-inlet combinations at high angles of attack. Calculations for isolated wings show the formation of a leading-edge vortex. At sufficiently high angles of attack, the lift distribution over the wing begins to oscillate in time. Calculations for wings subjected to a ramp motion reveal substantially higher lift loads prior to stall than for the static fixed angle-of-attack conditions. The results for wing-body-inlet combinations show separated flow off the sharp inlet leading edge, vortex formation over wing-inlet interface region, and over the wing leading edge. The vortex core trajectory and the flowfield agree well qualitatively with the experimental results. The analysis shows near-periodic fluctuations in the sectional lift coefficients with time. A Fourier analysis of the sectional lift coefficients reveals the flowfield to be rich in discrete frequencies. Calculations have also been carried out for a vertical tail configuration, which indicates large lateral forces on the vertical tail due to interaction between the vertical tail and the vortical flow off the wing-body-inlet configuration.