This project proposes to study Magneto-Rotational Instabilities in order to give an analogy with accretion disks.

When talking about origins, astrophysics has proved and observed that planets are created within a cloud of dust, ice and gas collapsing and orbiting onto a new-born star. As it collapses, the cloud is shaping itself into a disk where the planets, asteroids, comets are created. This disk is called an accretion disk. Even if the process of creation of planets (and smaller bodies) is known, the initiation of the process is still a non-answered question. The most promising solution is that magneto rotational instabilities (MRI) are responsible. Those instabilities, caused by both the rotation of the disk and the electromagnetic field of the star, are creating denser areas, then the gravitational forces do the rest. Those instabilities are called Magneto-Rotational Instabilities (MRI) and are the key point of this project.

To generate MRI, a fluid dynamic experiment system known as Taylor-Couette system is designed and built. The Taylor-Couette system is composed of two intricated cylinders separated by a gap in which a complex fluid is placed. A complex fluid does not have the same properties than a Newtonian fluid (like water): it acts like a solid when a force is applied to it. The two cylinders rotates around their common central axis, a flow is thus generated. The goal of this project is to observe instabilities in this flow. Instabilities are created by pushing the rotation speed beyond the limit of a linear behavior of the flow. Hence the flow sees the apparition of instabilities to restore its balance. Secondly, another system is created. This system shall be based on the principle of Savonius wind turbines. It is composed of two concave blades positioned so that the flow driven by one of them passes in the middle and strikes the second blade which drives the flow. However, the Savonius Module does not generate a TC flow and, since it has never been done before, the observed instabilities are quite different.

The prototype is 3D printed in plastic. It permits a great precision and a low cost. The reason is to be able to create reliable systems to equip small labs at a lower cost, hence helping researchers to work on complex flow instabilities. Precision, stability, robustness, reliability and affordability are the most important criterions in such module. Indeed, instabilities may not appear if the two cylinders or he two blades are not perfectly aligned. The prototype rotates due to a DC motor driven by an Arduino card controls the rotation of the experiment system using PWM (pulse width modulation. This choice of construction is thought to recreate as closely as possible the environment to observe instabilities to make the analogy with the accretion disks.


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