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題 名 | Laboratory Studies of Particle Dispersion in Two-Dimensional Turbulence=質點在二維紊流場中的擴散特性 |
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作 者 | 曾若玄; | 書刊名 | 力學 |
卷 期 | 11:1 1995.03[民84.03] |
頁 次 | 頁55-62 |
分類號 | 440.137 |
關鍵詞 | 擾流擴散; 二維紊流; 拉氏統計特性; 渦流擴散係數; Turbulent diffusion; Two-dimensional turbulence; Lagrangian statistics; Eddy diffusivity; |
語 文 | 英文(English) |
中文摘要 | 本文是以一結合實驗與數值計算的方法研究質點在一近似二維紊流場中的拉氏擴 散特性。研究結果發現在初始擴散階段時,所求得的絕對擴散距離以及渦流擴散係數值與古 典的擴散理論值相當吻合。另一方面,在較長時間之後,所求得的擴散特性則與理論結果有 差異,這顯然是由於紊流場的強度隨著時間而減弱(或不穩定性)的緣故。如果計算過程予 以適當修正, 亦即根據質點在 t=0 與 t=T ( T 是拉氏積分時間尺度)的平均動能分別來 推算初始階段與長時間階段的擴散特性,則上述差異將可大幅改善。最後,本研究所求得的 能譜斜率大約為 -2, 這與過去海洋表層或次表層浮標飄流觀測所得之拉氏能譜斜率頗為近 似。 |
英文摘要 | The absolute dispersion, Lagrangian velocity correlations, eddy diffusivity, structure function, and energy spectra characteristics of a quasi-two-dimensional turbulent flows are investigated in this study using a combined experimental-numerical technique. Experimented results, especially those for the absolute dispersion and eddy diffusivity and their asymptotic laws in the initial dispersion regime, correlate well with the classical diffusion-theory. On the other hand, the calculated Lagrangian statistics at large times are somewhat inconsistent with the predicted results due to nonstationarity of turbulence. This discrepancy can be substantially reduced if the dispersion analyses are based on the mean particles energy at t=0 and t=T (T is the Lagrangian integral time scale), respectively, for small and large times regimes. Furthermore, the slope of the Lagrangian energy spectrum beyond the cut-off frequency is close to -2, which is similar to previous observational results of Lagrangian velocity spectra as deduced from surface or subsurface drifters in the ocean. |
本系統中英文摘要資訊取自各篇刊載內容。