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Improvement of the SPH method for multiphase flows application to the emergency water landing of aircrafts : application to the emergency water landing of aircrafts

Abstract : This thesis focuses on the improvement of the SPH method for multiphase flows, and its application to emergency landing of aircrafts. This problem, also known as “ditching”, is characterized by violent flows resulting in large deformations of the free-surface. In addition, the ditching problem encompasses coupled evolutions of the different phases present during the impact, namely air, liquid water and, in extreme cases, water vapor. The SPH method is an excellent candidate for simulating such problems. Indeed, on the one hand, the absence of mesh within this method makes it easier to compute large deformations of the free-surface, completely eliminating the problem of mesh distortion, unlike other classical numerical methods such as Finite Elements. On the other hand, the SPH method naturally lends itself to the simulation of multiphase flows due to its Lagrangian formalism. The absence of convective terms within the SPH equations prevents the existence of numerical diffusion at the interface between fluids, eliminating the traditional need for interface capture schemes. During this thesis, first a new explicit weakly-compressible SPH model was developed, capable of simulating multiphase flows at high density ratios, possibly in the presence of a freesurface, while producing pressure fields without spurious oscillations. A study of the numerical stability of this model was conducted, resulting in a heuristic definition of the maximum stable time steps as a function of the sound speed ratio of the fluids involved. Then, the model was validated and compared to a Riemann-SPH scheme, in terms of stability domain, pressure fields and numerical diffusion. Finally, as part of the European SARAH project, the SPH method was applied to the problem of aircraft ditching under real impact velocity conditions. Experiments conducted by other partners have demonstrated the existence of cavitation at certain impact speeds. As a result, a numerical cavitation capturing technique was introduced in this thesis. Finally, 2D and 3D SPH simulations yielded a satisfactory agreement between the experiments and our numerical results.
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Submitted on : Friday, October 23, 2020 - 11:30:15 AM
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Imadeddine Hammani. Improvement of the SPH method for multiphase flows application to the emergency water landing of aircrafts : application to the emergency water landing of aircrafts. Reactive fluid environment. École centrale de Nantes, 2020. English. ⟨NNT : 2020ECDN0001⟩. ⟨tel-02976070⟩

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