基于Plateau-Rayleigh不稳定性探讨水柱与激光光环的依赖关系

Relationship Between Water Jet and Laser Ring Based on Plateau-Rayleigh Instability

在低流速条件下,当自由下落的水流落在刚性平面上时,如果水柱与平面的接触点被激光照亮,可以观察到若干环绕在水柱上的光环。实验证明,接触点附近的稳定波纹结构是形成水柱光环的必要条件。根据伯努利方程和由Plateau-Rayleigh不稳定性理论得到的扰动波传播的色散关系,建立波纹稳定方程,进而通过实验探究环绕水柱的光环的性质。理论和实验结果表明,光环的疏密、亮度和数量与水柱的下落高度和初始流速、刚性平面种类以及俯视角度有直接关系。光环随着水柱的下落高度和初始流速的增大而变得密集。激光在刚性平面损失的能量越少,则光环越亮。存在一个观察光环的合适俯视角度区间,俯视角度越大,观察到的光环越多,因此观察光环时要尽量俯视。

When a water jet freely falls onto a rigid plane with a low flow rate, light rings around the water jet can be observed if the point that the water jet contacts with the plane is illuminated by a laser beam. It is proved experimentally that stable ripple structures surrounding the contact point are essential to form the light rings of water jet. The equation of corrugated stability can be established based on the Bernoulli＇ s equation and the dispersion relationship of disturbance wave propagation derived by the Plateau Rayleigh instability theory, and then experiments are designed to investigate the properties of the light rings of water jet. The theoretical and experimental results show that the spacing, brightness and quantity of the light rings are straightly related to the falling height and the initial flow velocity of the water jet, the variety of the rigid plane and the depression angle. The spacing between the light rings becomes smaller with the increasing falling height and initial flow velocity of the water jet. The less the energy loss of laser in a rigid plane is, the brighter the light rings are. There is a proper depression angle range to observe the light rings. It is concluded that the bigger the depression angle is, the more the observed light rings are. Consequently it is better to overlook the light rings for a satisfied observation effect.