Ultrasound Measurement System with adaptive Sound Field for Turbulence Investigations in Liquid Metal Flows

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At many technical processes that involve liquid metals like steel production, semiconductor crystal growth or flow batteries, the melt flow has a remarkable influence on the product quality and the yield. Turbulent flows have the advantage of a high heat and material transport, but are, however, difficult to simulate numerically. Many applications raise multi-scale problems and require highly spatially resolving calculation grids for large and often complex geometries. Model experiments based on low-melting alloys as working fluid allow for the application of measurement techniques. They pave the way to investigate and understand the complex flow phenomena and hence open a perspective for a process optimization. The project aims for the realization of an ultrasound measurement system with a phased-controlled sound field and its qualification for the investigation of turbulent liquid metal flows in the fields of magnetohydrodynamics and thermal convection flows. In the first funding period the measurement system based on the phased-array principle allowing for sound focusing and steering was set up and characterized. Its functionality was demonstrated successfully at stationary liquid metal flows. The research activities shall be pursued consequently in the here applied second funding period. By improving the measurement properties, the possibilities for applications will be extended towards three-dimensional, highly-turbulent flows. The uncertainty of the lateral velocity component, which in particular is difficult to determine, shall be reduced by a correlation-based estimation algorithm. Using sending and receiving beam forming based on plane wave compounding, a high spatial resolution can be achieved with concurrent high temporal resolution. To cope with the large amount of incurring data, a data compression will be implemented allowing for a continuous measurement time of up to several minutes. As subject of investigation, a Rayleigh-Benard convection experiment will be pursued since the properties of the enhanced measurement system will allow for the first time to study the spatial and temporal structure of the large-scale convection herein. Such convection flows are of high relevancy for natural phenomena in geo- and astrophysics, but also for a multitude of industrial and technical flows. With regard to the energy transition towards sustainable energy, a contribution can be made towards the development of liquid-metal batteries as large-scale energy storage in particular.