Unsteady aerodynamics of nonslender delta wings, covering topics of shear layer instabilities, structure of nonslender vortices, breakdown, maneuvering wings, and fluid/structure interactions, are reviewed in this paper. Vortical flows develop at very low angles of attack, and form close to the wing surface. This results in strong interactions with the upper-surface boundary layer and in a pronounced dependence of the flow structure on Reynolds number. Vortex breakdown is observed to be much less abrupt compared to breakdown over slender wings. This results in challenges for the precise determination of vortex breakdown location and the interpretation of flow visualizations. One of the distinct features of nonslender wings is the location of the primary attachment zone outboard of the symmetry plane. Reattachment location correlates with the wing stall process and increased buffeting. Dramatic fluid/structure interactions emerge with increasing wing flexibility and result in substantial lift enhancement in the post-stall region. This recently discovered phenomenon appears to be a feature of nonslender wings. Rigid delta wings undergoing small amplitude oscillations in the post-stall region exhibit many similarities to flexible wings, including reattachment and reformation of the leading-edge vortices. Unusual self-excited roll oscillations have also been observed for free-to-roll nonslender wings.

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A high-order (up to 6th order) Navier-Stokes solver is coupled with a structural solver that decomposes the equations of three-dimensional elasticity into cross-sectional, smalldeformation and spanwise, large-deformation analyses for slender wings. The resulting high-fidelity aeroelastic solver is applied to the investigation of rigid, moderately flexible and highly flexible rectangular wings undergoing a pure plunging motion. Comparisons of the computed results with available experimental measurements demonstrate good agreement. A description of the complex interaction between the unsteady aerodynamics and the flexible wing structural dynamics is given. Connections between the results of this analysis and enhanced loads for the moderately flexible wing are made. Results presented suggest that an optimum amount of flexibility exists for the case of a plunging wing and is associated with wing motions where the wing tip deflection and wing root motion are in phase over much of the plunge cycle.

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The structure of the shear layer which emanates from the leading edge of a 76-deg sweep delta wing and forms the primary vortex is investigated numerically. The flow conditions are M v _ = 0.2, Re = 50,000 and angle of attack of 20.5 deg. Computational results are obtained using a Beam-Warming-type algorithm. The existence of a Kelvin-Helmholtz-type instability of the shear layer which emanates from the leading edge of the delta wing is demonstrated. A description is provided of the three-dimensional, unsteady behavior of the smallscale vortices associated with this instability. The numerical results are compared qualitatively with experimental flow visualizations exhibiting a similar behavior.

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