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題 名 | 數值模擬大氣邊界層內密閉牆之空氣二維流場=Numerical Simulation on Two Dimension Solid Wall in Atmospheric Boundary Layer |
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作 者 | 梁大慶; 陳鉅昌; | 書刊名 | 水土保持學報 |
卷 期 | 30:4 1998.12[民87.12] |
頁 次 | 頁269-278 |
分類號 | 440.137 |
關鍵詞 | 大氣邊界層; 數值模擬; 流場; 密閉牆; Atmospheric boundary layer; Numerical simulation; Flow field; Solid wall; |
語 文 | 中文(Chinese) |
中文摘要 | 本研究以數值計算模擬大氣邊界層內,近地表氣流通過直立密閉牆所發生流場的 變化狀況,以動量、連續方程式所推展出的數值黏性流場為基礎,在正交網格的計算程式採 用 MacCormack 之預測步 - 校正步的顯隱式法,以提高時變模擬之精確度, 同時以庫倫( Courant-Friedrichs-Lewy )條件確認結果之收歛性。本文中探討流場質點由於牆面之阻擋 所產生軌跡之改變,以及氣體在不同空間位置運動之方向和速度,並分析在網格中所設不同 位置追蹤點在計算時速度在時間的數值收歛性。其結果概述如下: (一)地表附近恆定來流迎向密閉牆,有渦流群之非恆定現象發生,於牆後存在一個較大橢 圓形順時針運動之氣流囊,及近地表牆前、後牆各有一個順、逆時針之小型氣流囊。 (二)近地表上游來流依速度與高度關係之 1/7 指數律之條件給定、 計算高度以 0 ∼ 5H 及水平距離 -3H ∼ 30H 為範圍,其中 H 為構造物邊高度。 計算所得之主氣流囊內迴流之 最大速度 0.269。迎風面牆頂附近具有最大的向上速度 0.783,並向四週漸減。 (三)距離 3H 處以後,流線開始向地表迴流。OH 之流線具最大垂直舉昇高度 1.44H 是為 最高,再依向上流線而漸減。 (四)牆後非恆定紊流狀況之影響,牆後數值計算之速度值較牆前難收歛。 |
英文摘要 | This research was to analysis numerically characteristics of two-dimensional turbulent flows around a vertical wall in atmospheric boundary layer. The theory based on the numerical viscous flow field which was inferred from momentum and continuity equations. For the purpose of getting better accuracy of simulation we took MacCormack explicit-implicit method in orthogonal mesh. Courant-friedrichs-Lewy condition was used to confirm converge during computing. The simulation will be carried out to describe the velocity and directions of air flow in any position, and to analysis the difference of particles moving tracks approaching to fence. Also compare the converge characteristics of different tracers in real time numerical computation. The results are summarized as follows: 1. The unsteady vortexes are generated by the steady inflow around a vertical wall. Main ellipse vortex is moving clockwise direction behind the wall. Another two smaller vortexes present in forward and backward where closing to wall and surface, which are in clockwise and counterclockwise. 2. Inflow velocity condition is given by 1/7 power law according to height. Target area is 0∼5H in height and -3H∼30H in horizontal distance. "H" presents the height of wall. After calculating the maximum velocity in opposite of main flow direction is 0.269, which occurred on main vortex area. The maximum velocity in vertical direction is 0.783 on the top forward surface of wall, and reducing velocity far from it. 3. Streamlines start moving toward to earth surface in 3H distance behind the wall. The largest particle moving distance is 1.44H of OH streamline in vertical direction. Higher streamline it is and less moving distance it gets. 4. During computing the velocity behind the wall is not easy converge than that in front of wall due to effect of unsteady and turbulent flow field behind the wall. |
本系統中英文摘要資訊取自各篇刊載內容。