Formation and Coarsening of Roll Waves in Shear Flows down an Inclined Rectangular Channel

Source: ICHE Conference Archive - https://mdi-de.baw.de/icheArchive

Three-dimensional CFD simulations with large displacement of the geometries using a connectivity-change moving mesh approach

This paper deals with three-dimensional (3D) numerical simulations involving 3D moving geometries with large displacements on unstructured meshes. Such simulations are of great value to industry, but remain very time-consuming. A robust moving mesh algorithm coupling an elasticity-like mesh deformation solution and mesh optimizations was proposed in previous works, which removes the need for global remeshing when performing large displacements. The optimizations, and in particular generalized edge/face swapping, preserve the initial quality of the mesh throughout the simulation. We propose to integrate an Arbitrary Lagrangian Eulerian compressible flow solver into this process to demonstrate its capabilities in a full CFD computation context. This solver relies on a local enforcement of the discrete geometric conservation law to preserve the order of accuracy of the time integration. The displacement of the geometries is either imposed, or driven by fluid–structure interaction (FSI). In the latter case, the six degrees of freedom approach for rigid bodies is considered. Finally, several 3D imposed-motion and FSI examples are given to validate the proposed approach, both in academic and industrial configurations

Anomalous Self-Generated Electrostatic Fields in Nanosecond Laser-Plasma Interaction

Electrostatic (E) fields associated with the interaction of a well-controlled, high-power, nanosecond laser pulse with an underdense plasma are diagnosed by proton radiography. Using a current 3D wave propagation code equipped with nonlinear and nonlocal hydrodynamics, we can model the measured E-fields that are driven by the laser ponderomotive force in the region where the laser undergoes filamentation. However, strong fields of up to 110 MV/m measured in the first millimeter of propagation cannot be reproduced in the simulations. This could point to the presence of unexpected strong thermal electron pressure gradients possibly linked to ion acoustic turbulence, thus emphasizing the need for the development of full kinetic collisional simulations in order to properly model laser-plasma interaction in these strongly nonlinear conditions.Comment: 12 pages, 4 figures, submitted to Physics of Plasma

On the Behaviour of Upwind Schemes in the Low Mach Number Limit: A Review

International audienceThis work is devoted to a review of different modifications proposed to enable compressible flow solvers to compute accurately flows near the incompressible limit. First the reasons of the failure of upwind solvers to obtain accurate solutions in the low Mach number regime are explained. Then different correction methods proposed in the literature are reviewed and discussed. This work concludes by some numerical experiments to illustrate the behaviour of the different methods

VMS Finite Element for MHD and Reduced-MHD in Tokamak Plasmas

The understanding of magnetohydrodynamic (MHD) instabilities is quite essential for the optimization of magnetically confined plasmas, a subject raising increasing interest as tokamak reactor design advances and projects such as ITER (International Thermonuclear Experimental Reactor) develop. Given the need and importance of numerically simulating and studying these instabilities, in this paper we report our effort in developing a stabilized full MHD numerical model to study tokamak plasmas in the frame of the Variational Multi-Scale formulation (VMS). Special attention is given to the plasma equilibrium calculation in limiter and x-point configurations. Several properties of the internal kink instability for a circular geometry were studied, e.g., dependence of the growth rate and mode sizes on the Reynolds Magnetic number and magnetic reconnection. The test cases were compared to other results numerically obtained before, as well as analytical developments. The effects of the VMS stabilization were rigorously verified in order to ensure a numerical stability without supressing the physical instabilities. The validation of this model gives rise to the possibility of simulating Edge-localized modes instabilities in the frame of full MHD equations

Relaxation based Godunov type scheme for low mach multiphase flows

The present work is devoted to the numerical simulation of multiphase flows with two non-miscible compressible fluids. In this regime, interfaces can be tracked (Front tracking) or reconstructed (VOF, MOF). For theses approaches, interface topology changes and wave transmissions are difficult points. Diffuse interface methods are simple way to overcome these difficulties. In this paper we show how the usual techniques based on pressure relaxation can be adapted for this context. We also derive a elegant way to applied low mach preconditioning. For a simplified model, this approach recover previous work of Guillard and Murrone