CFD And Experimental Study Of The Internal Flow Of Laterally Vibrated Droplet

The vibration of resonant droplet have relevance to a wide range of technological processes such as liquid- liquid extraction, synthesis of ceramic powders, crystal growth in microgravity. There are experimental and numerical simulation about the internal flow in a moving droplet have been extensively studied.Before the move of the droplet by the actuation forces, the contact force generated at the triple contact line will balance the actuation force. When the actuation force could not overcome the contact force, the contact line of droplet will not move. The internal flow in a droplet which contact line is fixed are rarely reported in the literature,thus to know the internal flow of a resonant droplet has important theoretical and practical value.This article’s simulation is based on VOF-CSF model, using Fluent CFD software to simulate the internal velocity field in a droplet at different resonant frequencies, and confirmed the correctness of the simulation results through experiments, the mainly work completed in this article are summarized as follows:This article established resonant droplet’s CFD model, having a reasonable division of the grid according to the calculation accuracy and computation time during simulate droplet’s vibration, setting the appropriate boundary conditions, establishing the control equations based on the VOF-CSF model during vibration, to achieve the numerical simulation of the velocity field in a droplet under the vibrated condition,Compared with experimental observation in a resonant droplet,the simulation results are confirmed right.This article study the internal flow mechnism inside the droplet at the first, second and third resonant frequency, observes the phase diagram, the total internal pressure and velocity field from the side and front view and draw internal flow lines in the droplet at different moments. The conclusions are: at first, the downward movement will be appeared in the top of the droplet at all resonance frequencies, after recovering the height,the droplet swinging around the shape, with the resonance frequency increasing, swings and deformation of droplets is also growing, during vibration, extreme left, extreme right, and top will be the maximum pressure area.In the first resonance frequency, the internal flow observed from side and front view is similar.There are a small and big two flow circuits on both sides of a droplet, two smaller flow circuits appear near the contact line. In the second resonance frequency, the internal flow is influenced by the Laplace force, the two flow circuits on the both sides gradually disappear with the vibration time.Two flow circuits near the contact line become bigger,the internal flow observed from the front is the same with the first resonance frequency.In the third resonance frequency, the phase change and the swing becomes more intense, the upper flow in the droplet becomes disorder, but in the vicinity of the contact line form the largest flow circuits.From the front view, the interal flow do not change a lot.There is a big flow circuits on each side and remains two smal er flow circuits near the contact line.Analyzing the internal flow inside droplet at three different resonance frequencies,it is found that the irregular flow in the droplet cause a deformation.The stronger the irregular flow, the greater the droplet deformation, resulting in rapid movements on the gradient hydrophobic surface.When the internal flow of a droplet on left and right sides is symmetrical, the droplet deformation will not occur. The internal flow at different resonant frequencies are the same without the influence of Laplace force. When the vibration begin, the leftmost and rightmost ends of the fluid at the horizontal diameter flow horizontal towards the inner, the top of the fluid flows downward.The leftmost and the rightmost of the fluid form two flow circuts near the contact line.The top fluid flow downward from the middle and then flow upwardly along the edge of droplet,forming two strong upward flow circuits.In the process of flowing downward from the middle,the fluid will flow downward to form two smaller downward flow circuits.Establishing self-assembly experimental setup to observe the internal flow of vibrated droplet.With the help of fluorescence CCD,the flow track of Rhodamine B is observed from the side view in the second resonance frequency.The result is fluorescent particles from the top of the droplets flow downward in the middle and then flow upward along the edge to form two strong upward flowcircits.