• PhD,

PhD Defense - Imadeddine HAMMANI - ED SPI

Improvement of the SPH method for multi-fluid flows and application to the emergency water landing of aircrafts

on January 31, 2020

Supervisor: David LE TOUZE

Laboratory: LHEEA

Friday 31 January at 2.00 pm at Centrale Nantes - Lecture Theatre B008

This thesis focuses on the improvement of the SPH method for multi-fluid flows, and its application to emergency water landing of aircrafts. This problem, also known as “ditching”, is characterized by violent and non-linear 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 multi-fluid 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 multi-fluid flows at high density ratios, possibly in the presence of a free-surface, 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.

Published on January 22, 2020 Updated on January 30, 2020