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

► A two-dimensional vector-field ultrasound Doppler velocimeter was developed. ► A high spatial and a high temporal resolution is obtained simultaneously. ► The velocity fields of unsteady magnetically-driven liquid metal flow were mapped. ► Frame rates of 30fps for a vector field of 24×24 vector arrows were achieved. We present a novel pulsed-wave ultrasound Doppler system for fluid flow investigations being able to determine two-dimensional vector fields of flow velocities. Electromagnetically-driven liquid metal flows appear as an attractive application field for such a measurement system. Two linear ultrasound transducer arrays each equipped with 25 transducer elements are used to measure the flow field in a square plane of 67×67 mm2. The application of advanced processing methods as a multi-beam operation, an interlaced echo signal acquisition and a segmental array technique enable high data acquisition rates and concurrently a high spatial resolution, which have not been obtained so far for flow measurements in liquid metals. The extended pulsing strategy and essential operation principles such as the multiplexing electronic concept will be presented within this paper. The capabilities of the measuring system make it suitable for investigations of non-transparent, turbulent flows. Here, we present measurements of liquid metal flows driven by a rotating magnetic field for demonstration purposes. The measuring setup realized here reveals details of the swirling fluid motion in a horizontal section of a cube. Frame acquisition rates up to 30fps were achieved for a complete two-dimensional flow mapping.