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標題: | 層化異重流於三維水槽之流動形貌分析 An Experimental Investigation of Density-stratified Gravity Currents in an Unconfined Tank |
作者: | Yi-Kai Chen 陳奕凱 |
指導教授: | 戴璽恆(Albert Dai) |
關鍵字: | 柱型異重流,層化現象,定界交換,福祿數,慣性區段, cylindrical gravity currents,density-stratified flow,lock-exchange,Froude number,inertial phase, |
出版年 : | 2020 |
學位: | 碩士 |
摘要: | 本研究探討具分層行為之柱狀異重流於三維非侷限環境中的運動現象,並透過定界交換水槽系統(lock-exchange)進行實驗。於慣性區段時,異重流的前端頭部位置(R_f)及時間(t)存在著〖R_f〗^2= 2F_I B_0^(1/2) (t+t_I)之冪次關係,其中F_I為慣性區段的福祿數,B_0為初始重流體的重力,t_I則為積分因子。結果顯示慣性區段的福祿數會隨著控制因子重力比(R_B)及密度比(R_ρ)而改變。在重力比固定之下,福祿數會隨著密度比減少而下降。在密度比固定之下,於下層主導(0 <R_B≤ 0.3)時福祿數會隨著重力比增加而下降,並在過渡區域(R_B= 0.3)時達到最小值;於上層主導(0.3 ≤R_B< 1)時福祿數則會平均落於1.2 至1.35之間。均質無分層行為的異重流則有最大的慣性段福祿數F_I= 1.39±0.01。異重流的流動形貌同樣與兩個控制因子有密切關聯,於下層主導時,分層異重流會因密度比不同而有分離流動或部分混合的流動現象;於上層主導強層化時(R_ρ→0),會出現下層流體先後被混合及上層流體超越的二次覆蓋現象;於上層主導弱層化時(R_ρ→1),會因分層流體之間劇烈混合而形成與均質異重流相似的流動形貌。另外,在過渡區域時會隨著密度比不同而分別出現與下層及上層主導類似的流動。最後,在與二維層化異重流的比較中,發現三維層化異重流會較快達到最大頭部速度並隨後產生劇烈減速。另外,三維層化異重流也會有較大的慣性段福祿數。 The purpose of this study is to investigate cylindrical gravity currents produced from a two-layer density-stratified buoyancy source in an unconfined laboratory setup. In the inertial phase of propagation, the relationship 〖R_f〗^2= 2F_I B_0^(1/2) (t+t_I) applies between the front location R_f and time t, where F_I is the Froude number in the inertial phase, B_0 is the total released buoyancy and t_I is the t-intercept. Experimental results showed that Froude number in the inertial phase depends on two controlling parameters, the buoyancy distribution parameter R_B, and the density difference ratio R_ρ. For a given buoyancy distribution parameter, the Froude number in the inertial phase decreases monotonically as the density difference ratio decreases. For a given density difference ratio, the Froude number in the inertial phase decreases as the buoyancy distribution parameter increases for flows dominated by the lower layer, 0 <R_B≤ 0.3, and has a local minimum for the transition region, R_B= 0.3. For flows dominated by the upper layer, 0.3 ≤R_B< 1, the Froude number in the inertial phase fell between 1.2 and 1.35. When the buoyancy source is homogeneous, the Froude number in the inertial phase has its maximum value at F_I= 1.39±0.01. Also, the flow morphology is found to depend on these two controlling parameters. For flows dominated by the lower layer, two layers would separately propagate or mixed partially due to different density difference ratio. For gravity currents that are produced from a strongly stratified source, R_ρ→0, and dominated by upper layer, the mixed layer and upper layer may override the leading lower layer sequentially. For gravity currents that are produced from a weakly stratified source, R_ρ→1, and dominated by upper layer, mixing between two layers is severe and immediate, leading to the flow morphology similar with the homogeneous gravity currents. Besides, both upper-layer-dominating and lower-layer-dominating phenomena occur when the buoyancy distribution parameter falls in the transition region. At last, in contrast with the two-dimensional density-stratified gravity currents, results showed that the cylindrical one would reach the maximum front velocity more rapidly, and afterwards decelerate dramatically. Meanwhile, cylindrical density-stratified gravity currents have larger Froude number in the inertial phase. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/78342 |
DOI: | 10.6342/NTU202002112 |
全文授權: | 有償授權 |
電子全文公開日期: | 2023-08-01 |
顯示於系所單位: | 工程科學及海洋工程學系 |
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