两种风向下单栋塑料大棚内自然通风流场模拟

Numerical simulation of airflow distribution inside a tunnel greenhouse under two typical outside wind directions

为分析塑料大棚的侧窗和山墙门对单栋塑料大棚内自然通风的影响,该文运用CFX流体动力学分析软件对简易单栋塑料大棚内的自然通风情况进行了三维稳态模拟。外界风向分别取平行于大棚屋脊和与屋脊夹角15°两种情况。模拟结果显示:当风向与屋脊平行时,室内流场在稳定状态时基本上沿屋脊的中心纵截面对称,室外气流从山墙门和两边侧窗的前半部分进入大棚内,从后半部分的侧窗处流出,气流在大棚中心地带的流速较高,而在侧窗附近流速较低。大棚顶部和后部气流变化比较复杂;在风向与屋脊成15°夹角情况下,室外气流从侧窗的迎风处、背风侧窗的前部和山墙门进入,从背风侧窗处流出,室内气流场有一个明显的偏转过程。从侧窗流入的气流和山墙门流入的气流相遇后在大棚内形成了各种程度的涡流,使得大棚内气流分布较为复杂。室外风向对单栋塑料大棚内气流场的形态有明显影响。

A 3-D numerical simulation of natural ventilation process in a tunnel type greenhouse was performed with the help of software CFX to investigate the influence of wind direction outside on the airflow pattern inside and how the openings, door and side openings acted when the natural ventilation process was stable. The simulation was carried out under two typical wind directions: parallel and 15° to the greenhouse ridge, respectively. Result shows that on the condition of wind direction outside parallel to the greenhouse ridge, airflow enters into the greenhouse through frontispiece-open and the first half of the side windows, and departs from the remaining part of the side-windows. The overall airflow rates reach comparatively higher at tunnel central area and lower at the vicinity of sidewalls, the end part and top of the tunnel reveal many complex airflow patterns; Under the condition of wind direction 15° to tunnel ridge, air flows in mostly from the windward side opening and the frontispiece-open, departs from the leeward of side opening, there is an overall deflexion of the main current stream inside and various vortices are formed to produce the collision of airflow between sidewalls and air current, which makes airflow much more complex. The direction of wind outside has a major effect on the airflow pattern inside the tunnel greenhouse.