純水層流液柱噴流於斜向對撞後所形成之液頁流場之實驗與理論研究

A Combined Experimental and Theoretical Investiation of Fluid Sheets Flow generated by Obliquely Colliding Laminar Water Jets

余傳濬(Chuan-Chun Yu)

指導教授 ： 王興華

國立臺灣大學/工學院/機械工程學研究所/碩士(2007年)

https://doi.org/10.6342/NTU.2007.02019

摘要

本研究旨在深入探討既存已久霧化技術中，衝擊式液頁流場的根本成形原則與原理。並且引入微小尺寸液柱的新式碰撞條件，希冀藉此檢視典式理論於微小尺寸下的適用性。此外以新思維的模式思考近年才被提出的新型態流場─魚骨結構流場的成形條件與驗證，亦是本研究的主旨之一。而其研究方法為以結合實驗與理論的方式，探討於室溫室壓下微小純水液柱碰撞後所形成的液頁流場特性，並試著從其所顯示的各式物理現象，推敲出可能的物理原則。而其探討主題主要可分成三個部分:

(1)軸對稱碰撞液頁特性探討
(i)液頁型態:此處以無因次參數(We 、Re )探討液頁型態的成形情形。研究結果除了觀察到了多數典型型態的液頁流場之外，還進一步發現新型態的液頁流場─半穩定液緣非封閉式水練。並於文中提供了近年才剛被提出的震盪流流場的流續流動時序圖，以補足前人文獻僅用文字敘述的不足處。
(ii)液頁動力分析:
本研究首次導入以液柱動量的觀點，分析液頁成形的特性。而研究結果驗證了早期學者Taylor【7】所提出的液頁可能成形原理
(iii)液頁幾何:
研究結果發現，典式理論所提供的液頁輪廓預測理論於微小尺寸碰撞的條件下的預測準確度為有條件的適用；而探討液頁成形指標的液頁長寬比值於理論上僅與液柱碰撞角有關，而與液柱流速、尺寸無關。然而實際上液頁長寬比卻是會隨之改變。對此本文亦提出幾個可能的原因供參考之。

(2)非軸對稱碰撞液頁特性探討
(i)液頁型態:
本研究於此種液柱碰撞方式中，成功地觀察到魚骨結構流場的存在。當碰撞角度為60∘時，該流場的出現範圍為250

關鍵字

液頁 ； 液頁長寬比 ； 液頁型態 ； 軸對稱碰撞 ； 非軸對稱碰撞

並列摘要

The objective of this investigation is study the principle of classic atomization engineering of the impinge type of liquid sheet in great depth .and the attempts would be made to introduce the collide condition of new form in micro scale of liquid jets. Our aim is to examine the applicability of the classic theory of fluid sheets in the above condition, and discuss the formation condition of a new type of flow named fishbones. And the works is a combined experimental and theoretical investigation of fluid sheets flow generated by obliquely colliding laminar water jets in atmosphere environment. This investigation is mainly divided into three parts:

(1) The characteristics of fluid sheet flows formed by symmetric collision:

(i) fluid sheet types
The works is using method of dimensional analysis(Rej、Wej) to study the characteristics of fluid sheet types. In addition to several classic fluid sheet types, we discover a new type of fluid sheets called unclosed fluid chain with meta-stable rim. In addition , this research have provided the flow pattern of oscillating stream , despite the flow has been proposed by Bush and Hasha【24】in 2004. But they only had word statement without any flow pattern presented in their report.

(ii)dynamic analysis of fluid sheet flows:
The research is firstly introduce the aspect of the momentum of liquid jet to study

the characteristic of fluid sheet formation. And the results clearly demonstrate that the hypothesis of fluid sheet formation can be examined by experiment which has been proposed by Taylor【7】in 1960.

(iii) fluid sheet geometry
In these section, the classic fluid sheet shape theory in the micro-scale liquid jet impingement condition has been investigated. And the results have been demonstrated that the agreement of classical fluid sheet shape theory is conditional accuracy. And it has confirmed that the theoretical fluid sheets length to width ratio only vary with impingement angle, and the reality fluid sheets length to width ratio well vary with liquid jet velocity and jet diameter.

(2) The characteristics of fluid sheet flows formed by asymmetric collision:

(i) fluid sheets types
In an asymmetric collision, the fishbone flow has been observed .The limited parameter regine( 2θ=90∘, 250

並列關鍵字

fluid sheets ； fluid sheets length to width ratio ； symmetric collision ； asymmetric collision ； types of fluid sheets

參考文獻

【3】Rayleigh, L., “Investigation of the character of the equilibrium of an incompressible heavy fluid of variable density.”, Pro. R. Soc. Lond.ⅩⅣ, pp. 170-177, 1883.

【4】Taylor, G. I., “ The instability of liquid surfaces when accelerated in a direction perpendicular to their planes. Ⅰ”, Pro. R. Soc. Lond. A 202, pp. 192-196, 1950.

【5】Taylor, G. I., “ The dynamics of thin sheet of fluid. Ⅱ Waves on fluid sheets.”, Pro. R. Soc. Lond. A 253, pp. 296-312, 1959.

【6】Taylor, G. I., “The dynamics of thin sheets of fluid. Ⅲ Disintegration of fluid sheets. ”, Pro. R. Soc. Lond. A 253, pp. 313-321, 1959.

【7】Taylor, G. I., “ Formation of thein flat sheets of water. ” , Prov. R. Soc. Lond. A 254 , pp. 1-17 , 1960.