Numerical study of the vortical flow over a reverse delta wing

Reverse delta wings have been used in Lippisch type wing-in-ground crafts since the 1960's of the previos century, due to their stabilizing pitching moment close to ground. Previous studies showed that reverse delta wing behaves differently from a regular delta wing, either in terms of aerodynamic performance or flowfield structure. Up to this date only one study that includes a numerical simulation for the flow past a reverse delta wing have been published. In this thesis, we simulate numerically the unsteady flow past a reverse delta wing to understand better its aerodynamic performance, the structure of the flowfield 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 k$\omega$-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 coefficient $C_L$ for the flow past a delta wing at angle of attack $\alpha=20^{\circ}$. Before simulating numerically the flow past a reverse delta wing, we perform unsteady numerical simulations for the flow past a delta wing at angles of attack ranging from $5^{\circ}$ to $20^{\circ}$. We found that the lift of a reverse delta wing is unsteady even at angles of attack as low as $5^{\circ}$, differently from a delta wing. The power spectral density analysis shows that the time history of the lift coefficient $C_L$ 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 flow 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 almots the same.

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