動態微粒子串數值模擬

Abstract

本文利用商用軟體FLUENT來模擬二維微游泳器在流場中的游動情形，在此模擬中，藉由導入用戶定義函數(user define function)來操控微游泳器，使它做週期性的震盪，文中以震盪角度、頻率以及微游泳器型態這三個參數，並配合流體力學的史特豪數(Strouhal number)，以試誤的方式來分析微游泳器的震盪效率，並引用之前的文獻分析粒子串斷裂的方式來推測微游泳器的斷裂處。 模擬結果顯示，改變頻率只會改變微游泳器的遊動快慢，對於史特豪數大小的影響不是很顯著，這意味著改變頻率對於效率無顯著的提升。提升震盪角度會讓史特豪數降低，這意味著該微游泳器效率越來越好，但震盪角度超過70度則史特豪數又會開始上升。型態上，微游泳器越細長，史特豪數越低，且1L(N-1)S型態的微游泳器有較小的史特豪數。 斷裂預測方面，我們發現，微游泳器發生斷裂的地方會在尾端兩顆，因為尾端兩顆所受到的阻力差異極大，且微游泳器在角度為0度時會受到最大的流體阻力，因在該時候的角速度為最高。

In this paper, we simulate the swimming motion of micro swimmers in two dimension. We control the behavior of micro swimmers by UDF and make it oscillate periodically in a flow field. While in simulation, we take three parameters into account, frequency, angle of oscillating and the type of micro swimmers respectively. We use a dimensionless number to analysis the swimming efficiency of micro swimmers by try and error. And we speculate the rupture of micro swimmers by the method that previous paper had done. The simulation results show that Strouhal number will not be affected significantly by taking the frequency as the parameter. Increasing the angle of oscillating will decrease the number of Strouhal number, indicating a good efficiency with the micro swimmer. However, Strouhal number will start increasing when the angle of oscillating exceeds 70 degrees. By changing the type of micro swimmers, we find out that the longer the micro swimmer is, the lower the Strouhal number is. And type of 1L(N-1)S micro swimmers have a small Strouhal number. In the prediction of rupture, we find out that fracture usually occurs at the tail of micro swimmers because the drag forces between the end two particles in micro swimmers are different obviously. And the drag force will reach maximum when the micro swimmers oscillate to 0 degrees because of the maximum angular speed.