不同大小雙穴蝕氣泡破裂流場交互作用之試驗研究

Abstract

本研究利用兩組L型透明圓管放置於U型平台上旋轉，並改變轉軸旋轉頻率，以得到不同大小單一穴蝕氣泡，並將其中一顆氣泡藉由連通管移至另一試管之特定位置上。藉由調整兩顆氣泡間的距離，並使用壓力震波將氣泡震破，分析兩顆氣泡間的破裂行為，利用PIV所觀測的現象，於二顆氣泡中間形成液體帶狀區與低流速、高壓力情形。 本研究使用高速攝影機，以每秒8000張連續拍攝氣泡破裂過程的影像並分析，分析左大右小、右大左小各種不同間距氣泡破裂流場交互作用的特性。並應用質點影像測速法，進行流場交互作用的演變過程與速度量測分析。根據PIV計算結果，液體帶狀區如輻射狀往周邊散開，影響破裂後的流場運動，也產生兩氣泡之間的流體交替作用。氣泡間的壓力波相互影響而導致流場紊亂，流場紊亂處有Rayleigh-Taylor不穩定、Kelvin-Helmholtz不穩定渦流與Richtmyer-Meshkov不穩定現象發生。 兩顆氣泡均破裂的情況下，由實驗結果發現，距離參數γ值( )越小，氣泡表面外觀變形、推拉及交互作用明顯。另一方面，當氣泡位置設定不同，會影響所需要的破裂壓力，左側氣泡破裂的時間越短，液體噴流會跟著壓力波影響右側氣泡，使得兩顆均破裂所需壓力減少。此外，二氣泡破裂的複雜流場在本實驗中均可清楚展示與分析。

關鍵字：穴蝕、雙氣泡、質點影像測速法、交互作用

This study utilized two L-tubes filled with water, generated different size single cavitation bubbles by changing the U-shape platform’s angular velocity. One of the cavitation bubbles was moved to a specific stand-off distance from the other bubble through a connection tube. The bubble was collapsed by triggering a pressure pulse under different distance between bubbles. During the experiment, we analyzed the zone which has low velocity and high pressure was produced after bubble collapsed. A high speed camera (CCD) which can take 8000 images per second, was adopted to take sequential images of the different sized collapsed bubble flow in this study. The characteristics of the interaction of the different sized bubbles collapse flow were analyzed based on the recorded sequential images. The detail velocity fields of the interaction of the collapsed bubble flows were measured by particle image velocity (PIV) method. According to the results of PIV, movement of the liquid zone not only influences the motion of the flow fields, but also produces disturbe flow between the bubbles. The effect of the interaction of the pressure waves between two bubbles led to the disturbed flow field, resulted in the Rayleigh-Taylor instability, Kelvin-Helmholtz instability and Richtmyer-Meshkov instability. Experimental results show that the effect of changes on the bubble appearance, thrust and interactions increased as the distance parameter γ ( value decreased. On the other hand, the collapsing pressure would be effected by the different position of bubbles. The collapsing pressure is reducing when left bubble has less collapsed time. In addition, the complex phenomena of the collapsing flows of two different sized cavitation bubbles are presented and analyzed clearly.

Keywords： Cavitation, two bubbles, PIV,interaction