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High-agility aircraft often perform flight maneuvers at high angles of attack and angles of sideslip. For these configurations, a comprehension of the vortex development, interaction, and breakdown at sideslip conditions is crucial. In this study, two generic, low-aspect-ratio, hybrid-delta-wing configurations are investigated. A triple-delta-wing and a double-delta-wing configuration are discussed. Force and moment measurements, particle image velocimetry, and oil-flow visualization tests are conducted to resolve the vortex-dominated flowfield extensively. The flow separates at the sharp leading edges, and vortices are formed. For an angle of sideslip, the effective leading-edge sweep on the windward side is reduced and on the leeward side increased. This leads to a more stable vortex system on the leeward side and a destabilization on the windward side. Therefore, significant lateral instabilities occur at high angles of attack.

For an improvement of the flight stability characteristics of high-agility aircraft, the comprehension of the vortex development, behavior and break down is important. Therefore, numerical investigations on low aspect ratio, multiple-swept-wing configurations are performed in this study to analyze the influence of the numerical method on the vortex formation. The discussed configurations are based on a triple- and double-delta wing planform. Unsteady Reynolds-averaged Navier–Stokes (URANS) simulations and delayed detached eddy simulations (DDES) are performed for both configurations. The simulations are executed at Re $$= 3.0\times 10^6$$ = 3.0 × 10 6 , symmetric freestream conditions, and an angle of attack of $$\alpha = 16^\circ$$ α = 16 ∘ , for consistency with reference wind tunnel data. For the triple-delta-wing configuration, the results of the DDES show a satisfying accordance to the experiments compared to URANS, especially for the flow field and the pitching moment coefficient. For the double-delta-wing configuration, the URANS simulation provides reliable results with low deviation of the aerodynamic coefficients and high precision for the flow field development with respect to the experimental data.

The dependencies of numerical simulations regarding grid sensitivity and modelling error for vortex dominated flow need particular investigation. In this study, an extensive investigation on the grid sensitivity is conducted and the influence of different turbulence closures is analyzed. For this purpose, a triple-and a double-delta-wing configuration are considered. In a collaboration between the French National Centre for Scientific Research, the Centrale Nantes Engineering School and the Technical University of Munich, simulations were conducted to identify grid and turbulence closure sensitivities. For the grid sensitivity, a comparison of the global force and moment coefficients and of the local flow in the vortex core is shown. From this, it can be concluded that the local flow is more sensitive to grid adaptation than forces and moments. Furthermore, the double-delta-wing configuration seems to be more affected by grid sensitivity. The comparison of k-𝜔 shear stress model, delayed detached eddy simulation and different grids and background closures indicates a lower influence of grid sensitivity to delayed detached eddy simulations than to k-𝜔 shear stress models. A grid convergence represents an important parameter but for vortex dominated flows, it can only be achieved by a local convergence for the vortex core flow is of primary importance as vortex core flow characteristics strongly determines the accuracy of the moment prediction.