Theses (original) (raw)
Application de la Méthode de Boltzmann sur Réseau à l’Etude de la Propagation d’Ondes dans les Fluides
The Lattice Boltzmann Method (LBM) is applied in this thesis to study acoustic waves propagation and heat transfer in fluids. The work can be summarized in five parts: The first two sections deal with the basic mathematical formulations of the kinetic theory of gases and the numerical lattice Boltzmann approach. Numerical simulations are started in the third part. This part first presents the basic principles of acoustics and then gives a two-dimensional (2D) study of acoustic waves propagation in water. The waves are generated by a rectangular acoustic source vibrating at 200 kHz. The objective is to calculate the acoustic pressure and force produced in the near field, and then to inject the numerically calculated force into the LBM code used to produce the acoustic streaming flow. Given the importance of numerical studies used as data to perform experiments, the simulation of physical problems in three dimensions (3D) becomes a necessity to visualize the physical phenomenon much better than in 2D. Therefore, the three-dimensional lattice Boltzmann method is used in the fourth section to study the propagation of acoustic waves in water. The main objective of this numerical study is to show how waves generated by a point source and square and circular shaped sources propagate instantaneously in 3D, to calculate the acoustic pressure and to highlight the performance of LBM simulations. A comparison of the numerical results found with the analytical data is performed to validate the numerical approach used. The fifth part presents a 3D numerical study of the physical phenomena of ultrasound propagation in air, thermal convection and their interaction. Considering its advantages in terms of accuracy and computational efficiency over the pure LBM method, the hybrid method based on the LBM approach for the description of the hydrodynamic behavior of the fluid and the finite difference technique for the temperature calculation is introduced in this last part to investigate the improvement of the heat transfer by the ultrasound.
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