Translated Titles

Numweical Simulation of Bubble Collapse near Solid Boundaries



Key Words

射流 ; 有限圓柱 ; 氣泡破裂 ; circular cylinder of finite length ; jet ; bubble collapse



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Chinese Abstract

本研究主要是以三維邊界元素法來模擬出水下爆炸氣泡在固體邊界時的變形情況。在本文中會將對於氣泡動力的一些基本理論和數值方法做一些詳細介紹,並用Rayleigh-Plesset 理論來驗証出其數值方法的準確性。在文章中的氣泡所處理的邊界條件有三個,分別是在無限流場、無限平板、有限圓柱,我們觀察出氣泡在這三種邊界的的破裂情況,並且各別有系統地比較出氣泡射流的速度。在結果上顯示出氣泡在無限流場的時候,其射流因為重力的作用關係,所以方向會是向上,而當氣泡在平板附近的時候,影響射流的因素分別為固體平板的吸引力和重力,所以固體平板的位置會直接影響到氣泡射流.最後所討論的邊界條件為有限圓柱,本文在這裡會針對不同的圓柱位置的時候,比較出氣泡底部節點的速度和最靠近氣泡的圓柱表面的壓力變化。在速度的比較上也可以發現出當氣泡位於圓柱下方的時候氣泡射流的速度會是最快的,而在圓柱上方時會是最慢的。而在壓力的比較上的話,發生最大壓力的時候都是在爆炸的一瞬間,而氣泡太靠近圓柱的情況下壓力會有不穩定的現象,如果將氣泡放遠一點的話,圓柱表面壓力不穩定的現象就不會發生。

English Abstract

By introducing the row-sum elimination method to avoid the calculation of the solid angle and by devising a new technique to calculate the tangential velocity at the nodes, a new three-dimensional boundary element method was developed to investigate the bubble collapse in a free flow field as well as near solid boundaries. The accuracy of the present model was verified by comparing the numerical results for the one-dimensional bubble pulsation with the solutions obtained from the Rayleigh-Plesset equation. The numerical results show that as bubble collapses in a free flow field, the formed bubble jet is in the opposite direction to the gravity. When the bubble collapses near a plane solid boundary, the direction of the jet depends on the gravity and the relative position of the bubble to the boundary. Under the same conditions, the jet velocity has its maximum value when the collapse occurs beneath the solid boundary; on the contrary, it has the minimum value as the bubble jet forms above a solid boundary. The effect of a circular cylinder of finite length on the bubble collapse is similar to that of a plane solid boundary. Finally, the effects of the initial bubble radius and pressure on the bubble jetting were also studied.

Topic Category 工學院 > 水利及海洋工程學系
工程學 > 水利工程
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