Numerical Investigation of the Influence of Ground Effect on the FV Aircraft

Abstract

In order to meet the growing market demands of quieter, more aerodynamically efficient aircrafts, manufacturers constantly strive to innovate and optimize their designs. Over the years however, the extent of innovation related to the conventional 'tubular fuselage' configurations have somewhat reached a stalemate as the gains obtained have only been marginal. It is for this reason, there has off-late been a surge in research pertaining to unconventional aircraft design and configurations. The Flying V (FV) is one such alternative that was conceptualized by J. Benad at TU Berlin along with the Future Projects Office (FPO) at Airbus Operations GmbH in Hamburg. Results obtained from past studies show a 25% improvement in the lift to drag ratio of the FV as compared to the NASA Common Research Model (CRM), which was set as the basis of comparison for a fixed wing aircraft configuration. So far, aerodynamic studies have only focused on the cruise performance of the FV without any emphasis on its low speed behavior. Conventional aircrafts use high lift devices like flaps and slats to improve stability and increase the amount of lift its wings produce at lower speeds. The FV however, has no such high lift device and solely relies on the lift produced by its wing to achieve a speed that is low enough to land safely. For this reason, this thesis aims to investigate the influence of ground proximity on the lift, drag and pitching moments of the FV which in turn affect its take-off and landing characteristics. Compressible RANS equations were solved with the k-omega SST turbulence model using ANSYS Fluent on a 4.6\% scaled model of the FV. The ground was numerically realized by employing the moving ground boundary condition equal in velocity to the free stream. Results from these simulations have shown a 11% reduction in the drag polar of the FV when closest to the ground as compared to when in unbounded flow. Additionally, the proximity to the ground causes an increase in lift and this allows the FV to touch down at 19 degrees while the maximum rotation angle during take-off is predicted to be about 13 degrees for a positive climb gradient when also considering the One-Engine-Idle (OEI) scenario. This corresponds to a lift to drag ratio equal to 10 and a lift-off lift coefficient of 0.56 approximately. The effect of ride height on the longitudinal stability of the FV showed that favorable pitching moments were obtained for angles of attack between 0 degrees and 5 degrees and for angles greater than 17.5 degrees. A near wake analysis was also performed for different angles of attack and at different heights from the ground to investigate the flow phenomena over the FV and the evolution of the wake downstream. No significant span wise flow is seen when the angle of attack is 0 degrees and the flow appears to travel parallel to the stream-wise direction. Additionally, in case of very high angles of attack, the flow streamlines confirm the occurrence of a large vortex emanating from the leading edge kink of the wing. When in unbounded flow a secondary vortex located inboard is produced at 17 degrees. The diameter of the tip vortex is seen to be greater than the inboard secondary vortex for an angle of attack equal to 17 degrees. At greater angles of attack, the secondary vortex is seen to grow in diameter as the height reduces.