Magneto-Fluid-Dynamic interaction phenomena for Aerospace applications

The Magneto-hydro-dynamics (MHD) is the discipline that studies the interactions between conductive fluids and applied magnetic fields. It integrates the phenomena of fluid dynamics and magnetism or electromagnetism, but also new ones specific to the interaction of the 2 domains. One of the remarkable features of this interaction is the mechanisms of induction to act without contact. One of the important properties that influence the intensity of electromagnetic forces is the electrical conductivity of the fluid. The dimensionless parameters which control the phenomena are generally 3; these are the classic Reynolds number (Re) in fluid mechanics, the interaction parameter (N) ratio of electromagnetic forces to inertia forces and the magnetic Reynolds number (Rm), ratio of the diffusion time of the magnetic field in the medium and the convection time. The proposed study is directed towards the analysis of 2 situations which a priori have little similarity but which in reality find their justifications in the sense that they both relate to flows around obstacles which are characterized by a wake whose configuration depends in particular on the magnetic Reynolds number. The analysis was performed digitally using the Finite Elements Method (FEM) with the software Comsol®. The first situation concerns the flow around a cylinder when the velocity field and the magnetic field are parallel to infinity. The analysis focused on the role of different parameters such as the influence of confinement, magnetic permeabilities relating to the fluid and the cylinder, and the magnetic Reynolds number. In all cases, the configuration of the wake, and in particular of von Karmann street, was analyzed either in terms of Strouhal number and in terms of drag exerted by the fluid on the cylinder. It has been observed in particular the existence of a critical value for the interaction parameter for which the von Karmann street disappears and is replaced by 2 vortices which remain attached to the cylinder. This critical value depends in particular on the magnetic Reynolds number. When this number becomes high the critical value of N has increased the vortices of von Karmann persist for high magnetic fields. In the second part of the thesis, the analysis method developed in Part I has been applied to the study of the Space propulsion system called Mini-Magnetosphere Plasma Propulsion (M2P2). The proposed system exploits the action of the solar wind, which is a completely dissociated hydrogen plasma made up of electrons and protons moving at high speed between 300 ÷ 800 km/s, this wind is therefore sensitive to the action of field magnetic. The method is based on the creation of a large-scale magnetic field transported by a plasma magnetized by a coil, to thus form a minimagnetosphere which deflects the solar wind as a sail would do it. This interaction generates a force to propel the spacecraft. Although low, the force applied over a long period of time makes it possible to reach speeds of several tens of km / s. The physics of the phenomenon can be compared, any scale kept, to the terrestrial magnetic field which protects the earth from solar winds. In this study, two specific aspects were considered. The first one concerns the operative conditions that allow the ejected plasma to be captured by the magnetic field, in this way inflating the sail. The second one concerns the calculation of the thrust that the wind exerts on the sail. The analysis has been performed resorting to the non-dimensional analysis on one side to reduce the computational burden of the FEM analysis, on the other side because it made it possible to perform at the same time the analysis of the real application and a possible experimental setup on ground.