Lorentz force velocimetry at high magnetic reynolds numbers

Lorentz force velocimetry is a contactless velocity measurement technique. The main idea behind this method can be expressed as follows: a magnet which is placed near a moving conducting fluid experiences the Lorentz force which is proportional to the conductor velocity. Since such measurements are non-intrusive they are especially appealing for industrial applications where people deal with hot and aggressive liquid metal flows. However, there is a fundamental restriction which limits an application area of the Lorentz force velocimetry. The restriction stems from the fact that at high velocities the magnetic field imposed by the magnet is expelled from the conducting media. As a result, the linear dependence of the Lorentz force on velocity is violated that leads to measurement errors. The aim of this work is to reveal fundamental aspects of the problems of this kind by conducting theoretical and mainly experimental research. The thesis consists of five main chapters. In the first one the topic of magnetohydrodynamics is introduced to a reader as well as the nuances of the Lorentz force velocimetry at finite magnetic Reynolds numbers Rem are explained. Next chapter presents a theoretical approach where the quasi-two dimensional model of the Lorentz force generation in a conducting slab is developed. The third chapter is concerned with the modeling experiment where a liquid metal flow is substituted with conducting solid rods. The results prove that if the magnetic field evolution is mainly controlled by advection, it leads to the statistical error in the Lorentz force measurements. The fourth chapter embraces the most important part of the work - experiments with a high-speed liquid sodium flow. Here for the first time the Lorentz force velocimetry was applied to study the flow whose velocity reaches 30 m/s. The experiment comprises both Lorentz force measurements and induced magnetic field measurements. Remarkably, a strong non-linear magnetic field expulsion was observed at Rem > 4. These data go in accordance with the Lorentz force saturation that occurs also at Rem ≈ 4. This study forms the basis of the Lorentz force velocimetry of the future and complements well already gained experience of measurements at low magnetic Reynolds numbers. The last chapter stresses the most important achievements in the actual research.