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Magnetic field dynamos-laboratory studies based on the riga dynamo facility

Exploitable results

The Riga dynamo facility is presently the only experimental set-up where the fluid flow induced excitation of a magnetic field can be studied in the laboratory. The project heavily contributed to the further exploitation of this facility. The upgrading consists of: - installation of an air cooling system, - increase of the motor power driving the propeller, - installation of a variety of magnetic field sensors inside and outside of the facility.
Velocity measurements of the sodium flow inside the dynamo facility have been performed by means of a local potential probe as well as by means of the ultrasonic Doppler velocimetry. The latter is applicable only to the outer fluid flow region where the flow is induced by the arising electromagnetic volume forces. The use of these measuring techniques to the case of the sodium flow in the Riga dynamo required special solutions for their adaptations.
The commercial pressure sensor KISTLER 6001 has been installed at the innermost wall of the Riga dynamo facility by means of a special adapter. This allowed measuring turbulent pressure fluctuations, the spectra of which agreed very well with the corresponding spectra of the magnetic field measurements.
Full numerical solutions have been developed in order to calculate the fluid flow and the related magnetic field distribution of the Riga dynamo experiment. Two-equation eddy-viscosity and full Reynolds-stress models have been used for the turbulence modelling. The coupled system was solved by a T-RANS based on large eddy simulation. In parallel, also kinematic dynamo calculations have been performed. The simulations showed a good agreement with the simplified model and with the experimental data.
A special magnetic coupler has been developed and built in order to replace the present mechanical seal at the Riga dynamo facility. The magnetic coupler works on a contactless action of magnetic forces in order to provide the corresponding torque from a motor driven rotating shaft to the facility shaft.
The inverse approach allows reconstructing internal flow fields out of external magnetic field measurements. This has been theoretically developed for the case of higher magnetic Reynolds numbers, and applied to the Riga dynamo facility. First demonstration examples showed the feasibility of this approach.