葉菜類採收機送風管之流場分析

Abstract

葉菜類作物為台灣國內重要之食用作物，主要種植於溫網室中，因其產量大需要機器幫忙採收。但現行之採收機無法有效地將切割後之葉菜吹起並收集。 因此本研究的目的為透過改變末端送風管之設計以增進葉菜收集效果。方法為先透過實際量測與模擬模型之數據比較，確立使用之紊流模型。再利用此紊流模型建立葉菜類採收機風管模型並修改細部外觀參數，並透過計算流體力學軟體模擬分析葉菜類採收機送風管出口之流場。藉此找到一較佳之風管外觀設定。 藉由實際量測與模擬結果比較，得知Realizable k-epsilon模型為較符合用於模擬採收機風管之紊流模型。後續的分析便以此紊流模型為基礎進行模擬。 模擬結果顯示減少副管數量可以有效提升出口流速增加率，且同樣副管數量下，固定副管間距或固定首尾副管位置對出口流速增加率影響甚小。此外，改變副管長度對出口流速增加率也無顯著之影響。而縮小副管出口直徑則可以大幅增加出口流速增加率。副管與水平面夾角為60度以及副管與主管夾角為150度時，風管也能夠有較佳之出口流速增加率。 綜合以上模擬結果，建立一自訂模型，其主管長度600 mm、直徑50 mm，副管長度95 mm、直徑12 mm，共有5副管並且副管間彼此距離105 mm，第一支副管距離入口90 mm，且與水平面夾角為60度，與主管夾角為150度。模擬結果顯示該模型出口流速增加率為735.216%，比原始風管模型增加745.92%。

Leafy vegetables are important food crops in Taiwan and are mainly grown in greenhouses and net houses. Because of its large output, machines are required to harvest the crops. However, current harvesters cannot effectively collect the cut leafy vegetables by blowing them. Accordingly, this study redesigned the air exit duct to improve collection efficiency of vegetable leaves. The turbulent flow model was first determined by comparing the actual measurement with the simulation model data. Next, the turbulent flow model was used to construct the air duct model of the harvester, appearance parameters were modified, and computational fluid dynamics software was employed to analyze whether the air duct model facilitates smooth air flow, thereby identifying optimal parametric values for the appearance of the air duct. By comparing the actual measurement with the simulation results, this study found that the realizable k-epsilon model is more suitable for simulating the turbulent flow model of the harvester duct, which was then used in subsequent analysis. The simulation results show that reducing the number of auxiliary pipes can effectively increase the outlet discharge velocity. With the same number of auxiliary pipes, maintaining a fixed distance between the auxiliary pipes or between the first and last auxiliary pipe had a negligible influence on outlet discharge velocity. In addition, modifying the length of the auxiliary pipe did not significantly increase the outlet discharge velocity. However, reducing the diameter of the outlet of the auxiliary pipe markedly increased the outlet discharge velocity. Marked increases in outlet discharge velocity were also observed when the auxiliary pipe was positioned 60 degrees to the horizontal plane and when the angle between the auxiliary pipe and the main pipe is 150 degrees. Based on the simulation results, a custom model was constructed, comprising a main pipe (length = 600 mm, diameter = 50 mm) and 5 auxiliary pipes (length = 95 mm, diameter = 12 mm). The distance between the auxiliary pipes was 105 mm. The first auxiliary pipe was 90 mm from the duct inlet and was positioned 60 degrees to the horizontal plane and 150 degrees to the main pipe. The simulation results show that the discharge velocity of the proposed model increased by 735.216%, an increase of 745.92% compared to the original model.