Numerical Study of The Vortical Flow Over a Reverse Delta Wing
Ahmed Osama Mahgoub
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Abstract
Reverse delta wings have been used in Lippisch type wing-in-ground crafts since the 1960's of the previous century, due to their stabilizing pitching moment close to ground. Previous studies showed that a reverse delta wing behaves dierently from a regular delta wing, either in terms of aerodynamic performance or oweld structure. Up to this date only one study that includes a numerical simulation for the ow past a reverse delta wing have been published. In this thesis, we simulate numerically the unsteady ow past a reverse delta wing to understand better its aerodynamic performance, the structure of the oweld and the unsteady phenomena associated. The numerical simulations are performed using ANSYS Fluent commercial software. The turbulence model used is Delayed Detached-Eddy in conjunction with the kω-SST as a RANS model. We selected the grid size and time step by performing a time step and grid sensitivity analysis using the power spectral density of the time history of the lift coecient C L for the ow past a delta wing at angle of attack α = 20 • . Before simulating numerically the ow past a reverse delta wing, we perform unsteady numerical simulations for the ow past a delta wing at angles of attack ranging from 5 • to 20 • . We found that the lift of a reverse delta wing is unsteady even at angles of attack as low as 5 • , dierently from a delta wing. The power spectral density analysis shows that the time history of the lift coecient C L is related to the time history of vortex shedding. The numerical simulations showed that over the leeward side of the reverse delta wing, the shear layer separating at the leading edge rolls into spanwise vortical structures that are convected downstream. As the vortical structures are convected, they alter the pressure distribution over the leeward side of the reverse delta wing. The results also showed that the tip vortex of a reverse delta wing is formed entirely by ow coming from the lower side of the wing. When comparing the performance of the delta wing against the reverse delta wing, at angles of attack below 10 • , both wings generated the same lift and drag, while at higher angles of attack, the reverse delta wing generated less lift and had less drag than the delta wing, but the lift-to-drag ratio for both wings is almost the same. Acknowledgement I would like to thank my supervisor, professor Luca Cortelezzi, for his help, he dedicated to me most of his time and always provided advises and suggestions for the improvement of this thesis. I would also like to thank the Department of Aerospace Sciences and Technology at Politecnico di Milano for providing me the computational resources necessary to complete this work.
