喜樹枝葉採收機之送風管流場分析

Abstract

喜樹枝葉採收機於田間採收時，由於被切割後之喜樹枝葉並不易被末端送風管所送出的風吹送入袋。因此本研究利用計算流體力學電腦模擬技術分析喜樹枝葉採收機之送風管流場且有效改變末端送風管之設計以利於喜樹枝葉吹送入袋。 本文先進行風洞實驗量測入口端與出口端之實際風速值，取得模擬之邊界條件，並計算其出口流速損失率。接著進行2D簡化模型之模擬，以找出合適之紊流模型，然後再進行3D實際尺寸模型之模擬，並改變其彎曲角度、支管長度、出口管徑及入口位置。 電腦模擬結果顯示零方程式紊流模型為喜樹枝葉採收機之送風管數值模擬較合適之紊流模型，並且建立實際尺寸之3D模擬之模型，證實與風洞實驗結果相當吻合。 再者，建立不同彎曲角度、支管長度、出口管徑及入口位置與出口流速損失率之關係。搭配實務上之考量，彎曲角度θ變更至15°之設計較佳，彎曲角度ω變更至75°之設計較佳，入口端位置位於側邊之設計較佳。此外，建立支管長度於20 cm內，對其出口流速損失率影響甚小之關係，以及出口管徑大小影響之出口風速與出風面積於實務上解決之法。

When a happy tree’s leaves and branches plucker is operated in field, it is not easy to blow the cut leaves and branches into a collecting bag by the wind provided from the end of ducts. Therefore, computational fluid dynamics technique is used in this study to analyze the flow field in air ducts for a happy tree’s leaves and branches plucker, and the end of ducts design is changed in order to blow the happy tree’s leaves and branches into a collecting bag easily. The inlet and outlet wind speeds from a wind tunnel will be obtained, and the loss rate of outlet velocity will then be calculated. A software called ANSYS/FLOTRAN CFD is used to build a 2D simplified model in order to find a suitable turbulence model. Subsequently, an actual 3D model will then be applied. Different outlet angles, outlet diameter sizes, outlet pipe lengths and inlet locations will be considered as parameters. In computer simulation, the zero-equation turbulence model was suitable for this air ducts in numerical simulation. An actual 3D model was confirmed to a good agreement with the experimental results. Furthermore, the study established the relationship between different parameters (outlet angles, outlet diameter sizes, outlet pipe lengths and inlet locations) and loss rates of outlet velocity. Considered with practical applications, the outlet angle θ changed to 15 degrees was a better choice. And the outlet angle ω changed to 75 degrees had a better result. Additionally, an outlet pipe length of 20 cm had a smaller influence on loss rates of outlet velocity. The outlet diameter size would affect wind areas and speeds in practical solutions. By different inlet locations simulation, it was found that the better location was in the side.