Department Magnetohydrodynamics
Research Topics:
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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
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Electromagnetic boundary layer control in conducting fluid flows
Experimental and numerical research on flow control by means of
electromagnetic forces in weakly conducting fluids (saltwater, electrolytes).
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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
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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.
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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
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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
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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
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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
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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
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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.
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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
Publications
Experimental facilities
