A7.2 - Two-Dimensional Ultrasound Doppler Velocimeter for Investigations of Liquid Metal Flows

SENSOR+TEST Conferences 2011
2011-06-07 - 2011-06-09
Proceedings SENSOR 2011
A7 - Ultrasonic Sensors II
S. Franke, H. Lieske, A. Fischer, L. Büttner, J. Czarske - Technische Universität Dresden (Germany), D. Räbiger, S. Eckert - Forschungszentrum Dresden-Rossendorf (Germany)
165 - 170


In the research area of magnetohydrodynamics the pulsed-wave ultrasound Doppler velocimetry (UDV) is a worthwhile measurement technique for flow field investigations of liquid metal flows. Several UDV instruments are available on the market. However, their capability for twodimensional mapping of flows is highly limited due to restricted number of scanning elements and low temporal resolution. Hence, we present an ultrasound Doppler velocimeter based on the application of ultrasound transducer arrays which allows measuring the in-plane velocity components of flow field in a measuring plane of 67 x 67 mm². It provides high measurement rates and concurrently a significant increased number of scanning lines with a high spatial resolution.
Our ultrasound velocimeter applies two linear ultrasound transducer arrays in an orthogonal arrangement. There, each array measures the inplane velocity component in propagation direction of ultrasound beam by electronic traversing. Each ultrasound array comprises 25 transducer elements each with a centre frequency of 8 MHz and a transducer element size of 2.5 x 5 mm². In operation two adjacent elements are combined to a square transducer pair of 5 x 5 mm² allowing a small spacing between the scanning lines of 2.5 mm and concurrently a low divergence of the ultrasound beam revealing a lateral resolution up to 2 mm.
The requirements for a high temporal resolution and a high number of scanning lines are opponent. To achieve a high measurement rate nevertheless, the measurement is parallelized as much as possible by simultaneous operation of four transducer pairs. Thereby a specific distance between the active transducer pairs avoids spatial crosstalk. For the same reason both arrays are actuated alternatively. The transducer excitation scheme is implemented by a fast multiplex electronics which is a proprietary development. Frame rates up to 33 Hz are achieved at pulse repetition rates of 1.5 kHz.
The performance of the system was examined at experiments with magnetic stirring. Therefore, rotating magnetic fields were applied to a cubic vessel filled with the liquid metal alloy GaInSn. The swirling flows caused by stationary as well as periodically reversed fields were measured and will be presented.