拱形塑料大棚风致干扰效应及风压特性研究

群体布置的拱形塑料大棚（简称群棚）棚间存在风致干扰效应，为了探明群棚干扰效应并建立考虑干扰效应的风荷载体型系数，基于Reynolds时均N-S方程和Realizable k-ε湍流模型，采用经验证的数值风洞方法研究了拱形塑料大棚单棚及群棚模型在不同风向角、不同棚间距下的表面风压特性。结果表明：拱棚群体布置引发干扰效应并改变风压特性，该效应具体表现为放大效应（群棚外围区域）和遮挡效应（群棚中间区域）；干扰效应受风向角及棚间距的影响较明显，整体随棚间距增大而减弱，并大致在10 m棚间距时趋于稳定。干扰效应整体削弱棚区风压通风能力，从利于风压通风角度提出了群棚园区规划布局建议，即棚身长轴方向宜与群棚所处地域夏季主导风向相垂直并适当增加棚间距。最后，以上述研究为基础，根据干扰效应分区域给出了群棚（矢跨比=3:8）便于设计使用的风荷载体型系数。处于群棚外围区域的拱棚，其风荷载体型系数具体为：当风向角为0时，风荷载体型系数在迎风面、中间棚顶、背风面、两侧山墙分别为+0.41、-0.78、-0.26、-0.48；当风向角为90°时，风荷载体型系数在迎风山墙、棚面分别为+0.36、-0.44。处于群棚中间区域的拱棚，其风荷载体型系数具体为：当风向角为0时，风荷载体型系数在迎风面、中间棚顶、背风面、两侧山墙分别为+0.30、-0.71、-0.26、-0.48；当风向角为90°时，风荷载体型系数在迎风山墙、棚面分别为+0.34、-0.35。研究结论：群体布置的拱形塑料大棚存在风致干扰效应，设计时宜考虑风致干扰效应引起的棚面风压变化。

Wind-induced interference effects and wind pressure characteristics of arched plastic greenhouses

Wind-induced interference effect commonly occurs among arched plastic greenhouse group. To describe such influence and finally determine the wind load shape coefficients considering the interference effects, we conducted a series of numerical simulations based on computational fluid dynamics (CFD). Combining the Reynolds-averaged N-S equations and the Realizable k-ε turbulence model, the surface wind pressure characteristics of the models for single greenhouse and greenhouse group under different wind direction angles and distances were studied separately. In combination with the actual production, 5 rows and 6 columns symmetrical layout was adopted as the greenhouse group's model with different gap distances (2, 4, 6, 8, 10 and 12 m) and wind direction angles (0, 30, 45, 60 and 90 degrees). In order to achieve quantitative analysis of the wind-induced interference effects, the interference factor was introduced in this paper as an important contrast parameter. According to the characteristics of the greenhouse structure, the greenhouse partition was reasonably set to realize the key research of wind pressure characteristics in wind-sensitive areas. In the numerical wind tunnel simulation, unstructured grids suitable for greenhouse group's model were used to divide the computational domain. The calculation parameters such as blocking ratio, inlet and outlet conditions, and near-wall treatments and so on were appropriately set. By comparing with wind tunnel test results of similar models, the present numerical simulations were verified. According to the simulation results, the arrangement of greenhouse group causes the wind-induced interference effects, which will change wind pressure characteristics of the greenhouses. The effects can result in amplification effects (the outer area of the greenhouse group) and the shielding effects (the middle area of the greenhouse group), among which the amplification effects threatens the safety of the structure and cannot be ignored. The interference effects is significantly affected by the wind direction angle and the gap distance, and specifically it decreases with the increase of distance, and tends to be stable when the distance between greenhouses is about 10 m. Based on the analysis of the variation law of the mean wind pressure coefficients and wind direction angles on the greenhouse group's roofs, it is obvious that the interference effects weakens the wind pressure ventilation ability of the greenhouse group as a whole. From the point of view of advantageous to wind pressure ventilation, the suggestions on planning and layout of the greenhouse group are put forward, that is, the long axis direction of the greenhouses should be perpendicular to the dominant wind direction in summer of the area where the greenhouse group is located and the gap distance should be increased appropriately. Finally, according to the wind-induced interference effects, the wind load shape coefficients for arched plastic greenhouses (the rise-span ratio is 3:8) are given, which are convenient for design. The wind load shape coefficients of greenhouses which are located in the outer area of the greenhouse group: At 0 wind direction angle, +0.41 on the windward side, -0.78 on the middle roof, -0.26 on the leeward side and -0.48 on both sides of gables; at 90 degrees wind direction angle, +0.36 on the windward gable, -0.44 on the roof. The wind load shape coefficients of greenhouses which are located in the middle area of the greenhouse group: At 0 wind direction angle, +0.30 on the windward side, -0.71 on the middle roof, -0.26 on the leeward side and -0.48 on both sides of gables; at 90 degrees wind direction angle, +0.34 on the windward gable, -0.35 on the roof. Wind-induced interference effects exists in arched plastic greenhouses arranged in group, and wind pressure changes on the greenhouses caused by wind-induced interference effects should be considered in design.