以面追蹤法及流體體積法數值模擬液滴碰撞之研究

Abstract

本文利用面追蹤法(front-tracking method)與流體體積法(VOF)數值模擬雙液滴碰撞，並且與實驗結果相互比較。在多相流(multiphase flow)的模擬中，面追蹤法的介面(front)設定是遵循實驗經驗所得，藉由指定中間液體薄膜破掉的時刻，使得模擬結果與實驗相符合。以流體體積法模擬中高速液滴碰撞時，需在介面處增加其黏性，減少因表面張力所產生的切線速度，讓液滴於拉扯過程中不至於破裂。流場模擬條件設定為兩相同尺寸的液滴正撞(head-on)於一大氣壓空氣中，溶液分別為水及十四烷，預測液滴在碰撞後的介面變化與現象。高速液滴碰撞情形下，我們使用流體體積法模擬三維流場中液滴於碰撞後的結果，評估應用套裝軟體CFD-ACE求解器在流體體積法模擬真實液滴碰撞流場的可行性。

This study focuses on numerical simulation for binary droplets collision. We compare the numerical results with the experimental ones by front-tracking method and volume of fluid (VOF) method. Front-tracking method is controlled artificially by prescribing the rupture of the inter-drop film in multiphase flow, and the simulation results are consistent with the experimental ones. In high-speed droplet collision, the surface tension force damping option in VOF increases the viscosity in the vicinity of the interface, which damps the capillary wave effect that is invariably generated at the interface by the surface tension. In the view of physics, the droplets are not supposed to rupture in the separation regime. Therefore, if the surface tension force damping option is selected, the droplet does not rupture during the collision. The simulation condition of head-on collision of binary equal-size droplets is set. Water and tetradecane are used to be the liquid phases to predict the phenomena of droplet collision under the atmosphere. We examine the feasibility of droplet collision simulation with VOF in CFD-ACE solver. The 3D simulation results of high-speed droplet collision are obtained by VOF.