声波团聚中尾流效应的理论研究

Theoretical Study of Acoustic Wake Effect in Acoustic Agglomeration

声波团聚是一项非常有潜力的颗粒物排放控制技术,最近的实验表明声波尾流效应是其中的重要机理。研究建立了Oseen条件下声波团聚中的尾流效应理论模型,并采用数值方法进行求解。研究了颗粒夹角、粒径和频率对声波尾流效应下的聚合速度的影响。计算结果表明,颗粒与声场的夹角对聚合速度影响很大,存在吸引和排斥两个区域。当夹角为0°~50°时,颗粒间存在强吸引作用,颗粒与声场平行时,聚合速度达到最大值;当夹角为50°～90°时,颗粒间表现为弱排斥作用,颗粒与声场垂直时,排斥速度最大。聚合速度随频率的增大而增加,但当频率超过某一临界值时,聚合速度基本保持不变;颗粒粒径越大,该临界频率越低。随着颗粒粒径的增大,聚合速度基本呈线性增加。

Acoustic agglomeration is a potential aerosol preconditioning process to reduce particulate matter emission. Recently, acoustic wake effect has been experimentally found to be an important hydrodynamic mechanism in acoustic agglomeration process. This paper presents a numerical simulation of the hydrodynamic interaction of aerosol particles due to acoustic wake effect under Oseen flow condition. The influence of the angle, included between the particle and acoustic field, particle size and acoustic frequency on particle convergence velocity due to acoustic wake effect was investigated. The particle convergence velocity varies greatly as the included angle changes. Strong attraction was found for particles with an included angle of 0° to 50°, and reaches a maximum at 0°. Outside this range, weak repulsion was found and reaches a maximum at 90° Particle convergence velocity increases with increasing acoustic frequency, but tends to approach a constant value at a threshold frequencies, which increases with the increase of particle sizes. In addition, it was found that with increasing particle size the particle convergence velocity increases proportionally.