Motion characteristics of a single bubble in liquid metal under a streamwise magnetic field

The three-dimensional motion trajectories of bubbles in liquid metal have been extensively measured under a horizontal magnetic field (HMF) using ultrasonic phased array technology. This study focuses on the case of a streamwise magnetic field (SMF). Experimental results show that the anisotropy of bubble oscillation in HMFs is not observed in the SMF. Under a weak SMF, single bubbles exhibit zigzag oscillation motion whose axis is along the streamwise direction. The oscillation frequency and amplitude decrease as the SMF intensity increases. As the SMF becomes stronger, the bubble suddenly begins to exhibit low-frequency oblique oscillations, the main axis of which deviates from the streamwise direction. Further increases in the SMF intensity produce an oblique straight-line motion, with the oblique oscillations suppressed by the magnetic field. Under the SMF, the terminal velocity of the bubbles initially increases when the magnetic interaction parameter is N<1, with the attenuation of the oscillation frequency being the dominant cause. However, the magnitude of velocity growth under the SMF is smaller than that in the case of an HMF. When N>1, the bubble terminal velocity steadily decreases and exhibits a similar trend to that under the HMF, along with an increase in the drag coefficient.