Two-dimensional ultrasound Doppler velocimeter for flow mapping of unsteady liquid metal flows

We present a novel ultrasound Doppler system for fluid flow engineering being able to determine two-dimensional, two-component velocity fields. Electromagnetically-driven liquid metal flows appear as an attractive application field for such a measuring system. Two linear ultrasound transducer arrays each equipped with 25 transducer elements are used to measure the flow field in a square plane of 67 x 67 mm². The application of advanced processing techniques like a simultaneous excitation of multiple transducer elements and a segmented array technique enable high data acquisition rates as well as a high spatial resolution, which have not been obtained so far for flow measurements in liquid metals. Essential operation principles such as the multiplexing electronic concept will be presented within this paper. The capabilities of the measuring system makes it suitable for investigations of nontransparent, turbulent flows. Here, we present measurements of liquid metal flows in a rotating magnetic field for demonstration purposes. The measuring setup realized here delivers details of the swirling fluid motion in a horizontal section of a cube. Frame acquisition rates up to 30 fps were achieved for a complete two-dimensional flow mapping.