垂直壁面附近单气泡运动特性可视化研究

Visualization of single bubble motion characteristics near vertical walls

为了明晰气泡在壁面附近的浮升行为及运动规律,采用高速摄影结合阴影图像处理算法,对水中近壁面气泡的迁移行为进行了可视化研究,探讨了不同初始离壁距离条件下气泡运动轨迹、形状和上升速度的变化规律。研究结果表明:在气泡上升的初始阶段,当气泡与壁面量纲一间距S^(*)≤1.4时,气泡趋向于壁面运动;当S^(*)≥2.05时,气泡远离壁面运动。在本研究的参数范围内,当S^(*)≤0.61时,气泡与壁面发生周期性碰撞,碰撞瞬间气泡水平速度发生反转,气泡形状由椭球形突变为球形;当S^(*)≥1.4时,气泡与壁面不再发生碰撞,气泡呈“之”字形振荡上升,上升轨迹近似于正弦曲线。随着气泡初始离壁距离进一步增加,气泡上升轨迹振荡的幅度减小,周期增大,壁面效应逐渐减弱;当气泡变形程度减小时,气泡纵横比的振幅变大。气泡水平速度呈现与气泡轨迹相同的变化趋势,振幅减小,周期增大;而气泡垂直速度基本不随初始离壁距离的改变而变化。当气泡与壁面不发生碰撞时,气泡垂直速度的振荡周期为水平速度振荡周期的1/2。

To clarify the rising behavior and motion patterns of bubbles near a wall,a visual investigation of bubble migration in close proximity to a vertical wall was conducted by high-speed photography and shadow image processing techniques.The variations in bubble trajectories,shapes and velocities at different initial wall distances were explored.The results show that during the initial stage of bubble ascent,when the dimensionless distance between the bubble and the wall S^(*)≤1.4,the bubble tends to move towards the wall.However,when S^(*)≥2.05,the bubble moves away from the wall.Within the investigated parameter range,when S^(*)≤0.61,the bubble exhibits periodic collisions with the wall,resulting in a momentary reversal of the horizontal velocity and a transition in shape from ellipsoidal to spherical.Conversely,when S^(*)≥1.4,no further collisions appear,and the bubble demonstrates a zigzagging motion resembling a sinusoidal trajectory.As the initial wall distance increases,the amplitude of oscillation in the bubble's trajectory decreases and the period of oscillation increases,indicating a weakening wall effect.Additionally,when the degree of bubble deformation decreases,the amplitude of oscillation in the bubble aspect ratio increases.The horizontal velocity of the bubble exhibits the same trend as the bubble trajectory with decreasing amplitude and increasing period.The vertical velocity shows minimal variation with changes in the initial wall distance.When the bubble no longer collides with the wall,the oscillation period of the vertical velocity is half of that of the horizontal velocity's oscillation period.