A Computational Fluid Dynamics Investigation of the 1303 UCAV Configuration with Deployable Rao Vortex Flaps

Abstract

A Computational Fluid Dynamics (CFD) study was conducted on an Unmanned Combat Air Vehicle (UCAV) configuration with deployable Rao Vortex Flaps (RVF). The UCAV configuration of interest to this study is a moderately swept, tail -less, flying wing. The numerical simulations were conducted on a UCAV model that was experimentally tested in two locations; in England using the QinetiQ 5 -meter wind tunnel and in the US at NAVAIR. In this analysis, the flaps were modeled as a 0.05 -inch thick plate with a d eflection angle of 28 degrees relative to the free -stream, and with a height of 5.44% relative to the mean average chord. All CFD computations were conducted using the NASA developed Reynolds -averaged Navier -Stokes flow solver USM3D. Complementary grid g eneration software, namely, Vgrid and Gridtool, were used to generate the unstructured girds used in the CFD analysis. The USM3D code has Euler and Navier -Stokes capabilities, as well as, laminar and turbulent capabilities; all of which were applied in thi s effort. A major objective of this CFD study was validation of the UCAV aerodynamic properties; C D, C L, C m, L/D and drag polar, obtained from the wind tunnel experiments reported in previous works. In an effort to complement the experimental analysis, CFD studies were conducted for angles of attack ranging from 0 to 14 degrees. Results indicated that good agreements were achieved between the CFD and experimental analyses. In addition, t his study confirmed that the RVF is very effective in reducing drag wh ile increasing the lift over drag performance at higher angles of attack. Results indicated that deploying the vortex flap at angles of attack above 8.5 degrees can potentially reduce C D and C m, and increase L/D, thus raising the upper limit of the UCAV’s flight envelope.