An aerodynamic study is conducted on two simplified geometries: the 25° Ahmed body with sharp edges [Ahm84] and the 25° Ahmed body with rounded edges [Ros16]. A hybrid RANS/LES approach is used: the DDES SST model. This model takes advantage of both RANS and LES formulations. In the near wall, in the unstuck boundary layers, the model works in RANS. When the flow is massively detached, the model formulation switches to LES, allowing the flow to be resolved more accurately. Numerical simulations have been performed and compared to the experimental data in [Ros16]. More details in [Del17]. The videos allow to observe the iso-surfaces of criterion $Q = 3 10^5$ as well as the differences in the flow topology around the two geometries studied.

[Amh84] Ahmed, S.R., Ramm, R. and Faltin, G.: Some salient features of the time-averaged ground vehicle wake, SAE Technical Paper Series, 840300, Detroit, (1984).
[Del17] Delassaux, F., Mortazavi, I., Herbert, V. and Ribes, C.: Numerical study of the flow around 25° Ahmed bodies with hybrid turbulence models. DLES11 will be published in the ERCOFTAC series book, 2017.
[Ros16] Rossitto, G., Sicot, C., Ferrand, V., Borée, J., and Harambat, F., ‘Influence of afterbody rounding on the pressure distribution over a fastback vehicle’, Experiments in Fluids 57:43, 2016.

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Direct numerical simulations of a three-dimensional incompressible flow around a hemisphere at Re=1000 were carried out using a vortex-penalisation method that allows simultaneous flow calculations in porous and fluid media. Comparisons (see image) between a solid hemisphere (left) and two hemispheres covered with a porous layer (centre) and a porous ring (right) have shown that the latter case has a 16% reduction in drag force compared to the uncontrolled case and ensures an overall regularisation of the flow, characterised by, among other things, a less chaotic wake with less developed vortex structures. doi.org/10.1016/j.euromechflu.2017.03.002

Simulation of a cylindrical shock representing a steam explosion in an experimental nuclear reactor. The simulation is done with the Lagrangian method presented in [1]. In the video on the left, we observe the evolution of the pressure profile, and thus the propagation of the shock wave, in the reactor pool. In the video on the right, we observe the evolution of a mesh over time on the same test case. It can be seen that the mesh deformations, which are inevitable when using Lagrangian methods, do not lead to mesh reversals and that the simulation of such phenomena can therefore be carried out with Lagrangian methods.

[1] Théo, Corot & Mercier, B. (2017). A new nodal solver for the two dimensional Lagrangian hydrodynamics. Journal of Computational Physics. . 10.1016/j.jcp.2017.09.053.