带电射流在电场扰动下的响应研究

The breakup of liquid jets is ubiquitous with rich underpinning physics and widespread applications. The natural breakup of liquid jets originates from small ambient perturbations, which can grow exponentially until amplitude as large as the jet radius is reached. For unelectrified inviscid jets, surface energy analysis shows that only axisymmetric perturbation is possibly unstable, and this mode is referred as varicose instability. For electrified jets, the presence of surface charge enables additional unstable modes, among which the most common one is the whipping instability that bends and stretches the charged jet that is responsible for the phenomena of electrospinning. Although the varicose and whipping instabilities of electrified jets have both been extensively studied separately, there is little attention paid to the combined effect of these two, which may lead to new jet breakup phenomena. At the same time, there is not a universal theory regarding viscous charged jet instabilities. This study investigates the dynamic response of electrified jets under electric field perturbations which were introduced by exciters driven by alternating voltage of sweeping frequency in order to solve the above mentioned problems.

射流的分裂随处可见，其蕴含的物理内容丰富，而且应用广泛。射流的自然分裂源于周围环境的微小扰动，不稳定的扰动随时间指数增长直至其大小与射流半径相当从而引发射流分裂。对于不带电非粘性的射流，表面能量分析显示只有轴对称的扰动才有可能是不稳定的，该不稳定性称为静脉曲张不稳定性（varicose instability）。对于带电的射流，表面电荷的存在引发了其他的不稳定性，其中最常见的是甩动不稳定性（whipping instability）, 在静电纺丝中射流被此不稳定性弯曲和拉伸。尽管静脉曲张和甩动不稳定性被单独的广泛研究，对于它们相互作用方面的研究相对较少，而它们的相互作用可能引发新的射流分裂现象。同时，现有文献中并没有一个关于带电粘性射流的不稳定性理论。本课题旨在研究带电射流在交流电场作用下的响应以解决上述问题。

射流的分裂是很常见的现象，其蕴含的物理内容丰富，而且应用广泛。射流的自然分裂源于周围环境的微小扰动，不稳定的扰动随时间指数增长直至其大小与射流半径相当从而引发射流分裂。对于不带电非粘性的射流，表面能量分析显示只有轴对称的扰动才有可能是不稳定的，该不稳定性称为静脉曲张不稳定性（varicose instability）。对于带电的射流，表面电荷的存在引发了其他的不稳定性，其中最常见的是甩动不稳定性（whipping instability）, 在静电纺丝中射流被此不稳定性弯曲和拉伸。尽管静脉曲张和甩动不稳定性被单独的广泛研究，对于它们相互作用方面的研究相对较少，而它们的相互作用可能引发新的射流分裂现象。同时，现有文献中并没有一个关于带电粘性射流的不稳定性理论。本课题旨在研究带电射流在交流电场作用下的响应以解决上述问题。在本项目中，我们施加正交扰动来改变和抑制空气中带电液体射流的不稳定性。研究了外加扰动的激励频率、幅度和相位差以及轴向电场等参数的影响。首次展示了在空气中具有线性增长横向振幅的稳定螺旋状鞭动结构。我们发现正交扰动能够叠加不同频率和相位的基本正弦信号，以创建复杂的类似李萨如图的图案模式。