声悬浮条件下黏性液滴的扇谐振荡规律研究

采用单轴式声悬浮方法研究了黏度μ =0.94-75.65 mPa·s的甘油-水溶液液滴的扇谐振荡规律. 发现一定阶数的振荡模式存在一定的临界黏度μ_c, 只有当μ < μ_c时, 该阶扇谐振荡才能被激发. 实验测定了声场调制幅度η = 0.23 时, l =2-9 阶扇谐振荡的临界黏度, 发现ln μ_c与l近似呈线性递减关系. 采用参数共振理论分析了黏性液滴的扇谐振荡过程, 发现激发扇谐振荡的液滴赤道半径扰动阈值h_c正比于液滴黏度μ, 并随l增大而增大, 因此扇谐振荡难以在高黏度和高阶模式下发生. 实验还发现, 各阶扇谐振荡的振幅和共振频率宽度随液滴黏度增大而减小, 黏度对液滴本征频率无明显影响.

Sectorial oscillation of acoustically levitated viscous drops

The sectorial oscillation of acoustically levitated viscous drops is investigated by applying a series of aqueous glycerol solutions (viscosityμ= 0.94—75.65 mPa·s).It is found that there exists a critical viscosityμ_c for a definite mode of sectorial oscillation,and that mode can be excited only when fj,< fic- The critical viscosities for the l = 2—9th mode sectorial oscillation are experimentally determined with a modulation amplitude to the acoustic field reachingη= 0.23.It is found that Inμ_c decreases approximately linearly with l.Analysis based on the parametric resonance theory indicates that in order to excite the sectorial oscillation,the equatorial radius of the drop must be perturbed over a threshold h_c,which is proportional to the viscosityμand increases with l.Therefore,the sectorial oscillations can hardly be excited to those drops with high viscosity and large oscillation modes.Both the amplitude and resonant modulating frequency width decrease with the enlargement of viscosity.No obvious effect of viscosity is found on the eigenfrequency of sectorial oscillation.