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

在许多涉及液态金属的技术过程中，如钢铁生产、半导体晶体生长或液流电池，熔体流动对产品质量和产量有着显著的影响。紊流具有高热量和高物质输运的优点，但难以进行数值模拟。许多应用程序提出了多尺度问题，并且需要对大型且通常复杂的几何图形进行高度空间解决的计算网格。基于低熔点合金作为工作流体的模型实验允许测量技术的应用。它们为研究和理解复杂的流动现象铺平了道路，从而为过程优化打开了一个视角。本课题旨在实现一种具有相控声场的超声测量系统，并使其具备在磁流体力学和热对流领域研究湍流液态金属流动的资格。在第一个资助阶段，建立了基于相控阵原理的声音聚焦和转向测量系统，并对其进行了表征。在固定的液态金属流动中成功地证明了其功能。因此，研究活动应在本申请的第二个资助期内进行。通过改进测量特性，应用的可能性将扩展到三维，高湍流。横向速度分量的不确定性尤其难以确定，应采用基于相关的估计算法来降低不确定性。采用基于平面波复合的发送和接收波束形成技术，可以在获得高空间分辨率的同时获得高时间分辨率。为了处理大量产生的数据，将实施数据压缩，允许长达几分钟的连续测量时间。由于增强的测量系统的特性将首次允许研究大尺度对流的时空结构，因此将进行瑞利-贝纳德对流实验作为研究对象。这种对流流不仅与地球和天体物理学中的自然现象密切相关，而且与许多工业和技术流也密切相关。关于向可持续能源的能源转型，可以对液态金属电池的发展做出贡献，特别是大规模储能。

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.