Magnetohydrodynamics - further research topics
- Crystal growth melt flow control using magnetic fields
A contactless control of melt convection is important for many crystal growth technologies. Typically steady magnetic fields are used to damp such flows and, in particular, turbulent fluctuations. Active flow driving forces due to alternating magnetic fields can be of stabilizing character, too.
- Instabilities in MHD flows around obstacles
Numerical and experimental work on the flow of a strongly conducting fluid around a circular cylinder in an external magnetic field; investigation of 2D- and 3D-instabilities.
- Liquid Metal Two-Phase Flows
- Investigation of the local properties of liquid metal two-phase flows (bubble generation, bubble dispersion, slip ratio, ...)
- Possibilities to control the two-phase flow characteristics by means of external electromagnetic fields
- Model experiments, measurements of quantities such as local void fraction, bubble velocity, chord length distribution of the bubbles, etc.
- Magnetic field self-excitation (Dynamo action)
Numerical simulations and optimization of the velocity profiles as well as development of magnetic field sensors for the Riga dynamo experiment. In this experiment, magnetic field self-excitation in a liquid metal flow was shown for the first time experimentally in November 1999.
- Measuring Techniques for Liquid Metals
- Development and application of measuring techniques to determine liquid metal flow quantities
- Fluid velocity: Mechano-optical Probe, Electrical Potential Probes, Ultrasonic Doppler Velocimetry
- Two-phase flows: Resistivity Probes, Ultrasonic Techniques, X-ray Radiography
- MHD Turbulence
- Investigation of the local turbulent structure of MHD channel flows
- Collecting experimental data to validate computer codes with implemented MHD turbulence models
- Measurements of the local velocity fluctuations, turbulence intensity, power spectra
- Velocity determination in conducting fluids via inverse method
If a moving electrically conducting liquid is exposed to an external magnetic field an electric potential and an additional magnetic field are produced. Having measured these fields at the fluid boundary and outside the fluid, respectively, the fluid velocity can be reconstructed by solving an inverse problem.
- MHD-Control of the direct melt extraction of intermetallic fibers
In the extraction process of fibres from the melt surface the induction heating and the rotation of the chill wheel cause turbulence and a wavy motion on the metal surface. Steady magnetic fields can be used to stabilise the process and allow the extraction of fibres with a diameter below 100 µm, which are of most interest for industrial application.
- Magnetic Levitation
Electromagnetic levitation is a method to treat metallic samples without contact to any wall. However, the process is often accompanied by instabilities like rotation or oscillation of the sample. The reasons for these instabilities have been analyzed and a method in order to stabilize the sample has been developed.
- Liquid metal model experiments
Applied processes in metallurgy or crystal growth are usually at temperatures above 700°C for which almost no measuring techniques exist. Therefore, several model experiments are performed since a variety of metallic melts exists up to 300°C which are able to reproduce the characteristic non-dimensional parameters of the real processes. On the other hand, measuring techniques are available in the department which allow to measure up to 300°C all interesting quantities like local velocities or pressures.
- Solidification of metallic alloys controlled by magnetic fields
The microstructure of a metallic alloy can be affected in a significant way due to the convection in the liquid phase during solidification. A time varying magnetic field can be applied to produce a flow field in the melt which influences the nucleation and growth processes. The aim of our research program is to find a strategy to refine the microstructure of castings by an optimal combination of magnetic field intensity, field frequency and cooling rate.