Hannes Beyer

Phased Array Ultrasound System for Planar Flow Mapping in Liquid Metals

Controllable magnetic fields can be used to optimize flows in technical and industrial processes involving liquid metals in order to improve quality and yield. However, experimental studies in magnetohydrodynamics often involve complex, turbulent flows and require planar, two-component (2c) velocity measurements through only one acoustical access. We present the phased array ultrasound Doppler velocimeter as a modular research platform for flow mapping in liquid metals. It combines the pulse wave Doppler method with the phased array technique to adaptively focus the ultrasound beam. This makes it possible to resolve smaller flow structures in planar measurements compared with fixed-beam sensors and enables 2c flow mapping with only one acoustical access via the cross beam technique. From simultaneously measured 2-D velocity fields, quantities for turbulence characterization can be derived. The capabilities of this measurement system are demonstrated through measurements in the alloy gallium-indium–tin at room temperature. The 2-D, 2c velocity measurements of a flow in a cubic vessel driven by a rotating magnetic field (RMF) with a spatial resolution of up to 2.2 mm are presented. The measurement results are in good agreement with a semianalytical simulation. As a highlight, two-point correlation functions of the velocity field for different magnitudes of the RMF are presented.

Instabilities and spin-up behaviour of a rotating magnetic field driven flow in a rectangular cavity

This study presents numerical simulations and experiments considering the flow of an electrically conducting fluid inside a cube driven by a rotating magnetic field (RMF). The investigations are focused on the spin-up, where a liquid metal (GaInSn) is suddenly exposed to an azimuthal body force generated by the RMF and the subsequent flow development. The numerical simulations rely on a semi-analytical expression for the induced electromagnetic force density in an electrically conducting medium inside a cuboid container with insulating walls. Velocity distributions in two perpendicular planes are measured using a novel dual-plane, two-component ultrasound array Doppler velocimeter with continuous data streaming, enabling long term measurements for investigating transient flows. This approach allows identifying the main emerging flow modes during the transition from stable to unstable flow regimes with exponentially growing velocity oscillations using the Proper Orthogonal Decomposition method. Characteris...

Modular ultrasound velocimeter for adaptive flow mapping in liquid metals

Understanding the complex interaction of conductive fluids and time-varying magnetic fields is the main goal of research in magnetohydrodynamics (MHD). Customized magnetic fields can be used to optimize flows in technical and industrial processes involving liquid metals. For example the performance of batteries with replaceable liquid electrolytes, such as zinc slurry energy storage systems, can be improved by magnetically influencing the flow of the electrolyte. However, necessary experimental studies are often limited by the performance of flow instrumentation for opaque liquids. We present a modular research platform for flow mapping in liquid metals, the phased array ultrasound Doppler velocimeter (PAUDV). It is based on the pulsed-wave ultrasound Doppler principle in combination with the phased array technique to provide an electrically steerable sound field, enabling novel applications in MHD research. The ability to dynamically focus the ultrasound beam allows to resolve smaller flow structures in planar measurements compared to fixed-beam sensors. The PAUDV can be applied to flows in narrow channels and two velocity components can be measured with only one acoustical access via the cross beam technique. Fast electrical traversing of the measurement volume allows to obtain and visualize turbulence statistics. A two-point correlation function can be retrieved by interleaving velocity measurements at two focal points of varying distance. The PAUDV consists of a modular electronics unit with up to eight beamformer cards, capable of driving a total of 256 channels. Each channel can be individually configured regarding the excitation pattern (three-level quantization, 64 samples) and the delay (1.6 ns resolution). Data acquisition and processing is implemented on multiple FPGAs, control and data visualization are performed on a PC. The capabilities of the modular research platform PAUDV are demonstrated on measurements in the alloy gallium-indium-tin at room temperature. Time resolved planar velocity vector maps are shown for a flow in a cubic vessel under the influence of a transient rotation magnetic field.

Modular research platform for adaptive flow mapping in liquid metals

Experimental studies in the field of magnetohydrodynamics (MHD) involving complex 3d flows are often limited by the performance of flow instrumentation for opaque liquids. We present a modular research platform for flow mapping in liquid metals, the phased array ultrasound Doppler velocimeter (PAUDV). It is based on the pulsed-wave ultrasound Doppler principle in combination with the phased array technique to provide an electrically steerable sound field, enabling novel applications in MHD research. The ability to dynamically focus and steer the ultrasound beam allows to resolve smaller flow structures compared to fixed-beam sensors. Two velocity components can be measured with only one acoustical access via the cross beam technique. Fast electrical traversing of the measurement volume allows to obtain and visualize turbulence statistics. A two-point correlation function can be retrieved by interleaving velocity measurements at two focal points of varying distance quasi-simultaneously.

Ultrasound flow mapping for the investigation of crystal growth

The production of high quality solar cells requires a deep understanding of the solidification process. Especially when time-dependent magnetic fields are used to improve the material and heat transfer in the melt, the resulting flow structures are complex and unsteady. Hence, numerical simulations are used to gain an insight into the melt flow. For the calibration of the numerical simulations, model experiments using liquid metals at room temperature are used. The melt flow is strongly influenced by the melt height, that constantly decreases during a solidification process. Hence, measuring the position and the shape of the solidification front is required for an understanding of the melt flow. Furthermore a comprehensive flow mapping of complex and unsteady flow phenomena is necessary. Commercial flow instrumentation systems usually utilize only one or a few single element probes that are operated strictly in sequential multiplex. This leads to low frame rates and limits their application to quasi-static flow fields.

Modular ultrasound platform for flow mapping in magnetohydrodynamics

Abstract Flow control based on time-dependent magnetic fields is used in various industrial processes involving liquid metals, i. e. during the solidification process of silicon to improve the quality and efficiency of wafers. In order to investigate the interactions between spatiotemporal-varying magnetic fields and conductive fluids numerical simulations are performed. The numerical models are verified by model experiments with opaque low-melting alloys. A suitable measurement technique for flow mapping in such model experiments is ultrasound Doppler velocimetry. In contrast to conventional systems employing transducers with fixed sound field our approach is to use a phased array with the ability to focus and steer its acoustic field. We present the Phased Array Ultrasound Doppler Velocimeter (PAUDV) for flow mapping in magnetohydrodynamics. With its custom host software for control and signal processing experiments that are flexible regarding the experimental setup can be defined.