Visualization on the shear-induced liquid metal recirculating flow in a cavity by ultrasonic method

In magnetohydrodynamic (MHD) experiments, it is particularly challenging to visualize the two-dimensional flow field inside opaque liquid metals while maintaining high spatiotemporal resolution. To address this, we present a multichannel pulsed ultrasonic Doppler velocimetry (MPUDV) system that utilizes two linear array ultrasonic sensors with different frequencies to measure fluid flow. The MPUDV system is employed to study the shear-induced liquid metal recirculating flow within the rectangular cavity under a transverse magnetic field, achieving a temporal resolution of 20 ms and a spatial resolution of 3 mm. The aspect ratio of the cavity is 1:1 and the spanwise aspect ratio is 0.1:1. The ranges of the Reynolds (Re), Hartmann (Ha) numbers are 12269 ≤ Re ≤ 22083, 0 ≤ Ha ≤ 809, respectively. We successfully visualize the two-dimensional flow field within the cavity. The experimental results reveal that the transverse magnetic field significantly suppresses recirculating flow and affects turbulence characteristics. The two-dimensionalization process of the central primary circulation eddy is accompanied by intense energy transport. The Lorentz and inertial forces jointly influence the turbulent kinetic energy (TKE). The TKE varies continuously with the Stuart number N, displaying a non-monotonic trend that shows a scaling law of N^2/5 when N < 1, while decrease dramatically with N larger than 1.