Verification of the multichannel pulsed ultrasonic Doppler velocimeter for the measurement of liquid metal flow

In the present study, by adopting the advantage of ultrasonic techniques, we developed a multichannel pulsed ultrasonic Doppler velocimetry (MPUDV) to measure the two-dimension-two-component (2D-2C) velocity fields of liquid metal flow. Due to the specially designed ultrasonic host and post-processing scheme, the MPUDV system can reach a high spatiotemporal resolution of 50 Hz and 3 mm in the measurement zone of 192x192\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$192 \times 192$$\end{document}mm2\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\text {mm}<^>{2}$$\end{document}. The experimental loop includes a cavity test section designed to establish a recirculating flow, thereby validating the accuracy of the MPUDV in measuring the velocity field with the well-developed particle image velocimetry (PIV). A comparison of the data obtained from the PIV and MPUDV methods revealed less than 3% differences exist in the 2D-2C velocity field between the two techniques during simultaneous measurements of the same flow field. This finding strongly demonstrates the reliability of the MPUDV method developed in this paper. Moreover, the ternary alloy GaInSn, which has a melting point below that of room temperature, was selected as the working liquid in the experimental loop to validate the efficacy of the MPUDV in measuring 2D-2C velocity fields. A series of tests were conducted in the cavity test section at varying Reynolds (Re) numbers, ranging from 9103 to 24,123. The measurements demonstrated that the MPUDV could accurately measure the flow structures, characterized by a central primary circulation eddy and two secondary eddies in the opaque liquid metal. Furthermore, comprehensive analyses of the velocity data obtained by the MPUDV were conducted. It was found that the vortex center of the primary circulating eddy and the size of the secondary eddies undergo significant alterations with varying Re numbers, attributed to the influence of the enhanced inertial forces on the flow within the cavity. It is therefore demonstrated that the current MPUDV methodology is applicable for measuring a 2D-2C velocity field in opaque liquid metal flows.