Research On Wind Resistance And Cooling Performance Of Large-Span M-Shaped Agricultural Greenhouse Structure

In order to improve the wind resistance and natural ventilation cooling performance of ordinary large-span arch greenhouses,reduce wind-caused disasters,and realize low-cost environmental regulation in summer,a large-span M-shaped greenhouse with superior wind resistance and cooling performance is proposed.In this paper,the overall wind pressure characteristics of M-shaped greenhouse and ordinary large-span arch greenhouse are analyzed under different wind direction angles by using computational fluid dynamics(CFD)method.The M-shaped greenhouse is optimized from the perspective of wind resistance.The research and comparative analysis of the ventilation and cooling performance of the optimized M-shaped greenhouse and the ordinary large-span arch greenhouse are carried out based on in-situ observation and validated simulation methods for wind and temperature coupling in the context of actual projects.The main research results of this paper are as follows.(1)Research on wind resistance performance of M-shaped greenhouse and ordinary large-span arch greenhouse under different wind direction anglesUnder 0° wind direction angle,vortices are generated in the V-shaped area of the Mshaped greenhouse,and the wind pressure coefficient of the top area is significantly smaller than ordinary large-span arch greenhouse due to the airflow blocking.The distribution of wind pressure coefficients outside the two types of greenhouses are basically the same under the wind direction angles of 30°,45°,60° and 90°.The wind pressure coefficients on the M-shaped greenhouse surface are significantly smaller than ordinary large-span arch greenhouse,especially at 0° wind direction angle.The wind pressure coefficient values and the action area are both smaller.The overall wind pressure coefficients of the roof gradually decrease with the increase of oblique wind direction angle.The wind pressure coefficients of M-shaped greenhouse are smaller.The wind pressure coefficients at 90° wind direction angle are the smallest,and the difference between ordinary large-span arch greenhouse and M-shaped greenhouse is small.The maximum wind load shape coefficients of M-shaped greenhouse and ordinary large-span arch greenhouse are-0.73 and-1.28 respectively.The maximum extreme wind pressure is 0.296 k Pa and 0.518 k Pa respectively.Taking the angle of V-shaped area as the variable to optimize the M-shaped greenhouse,it is suggested that the optimal angle is 95°combining with the calculation results of local and overall wind load shape coefficients.The research results prove that the M-shaped greenhouse has good wind resistance performance under different wind direction angles,which is important for disaster prevention of agricultural facilities.(2)Research on wind resistance performance of M-shaped greenhouse and ordinary large-span arch greenhouse under different opening methodsFor the four conditions with relatively large net wind pressure coefficients of windward side vent,leeward side vent,both sides vents and top vents,the internal and external wind pressure coefficients of M-shaped greenhouse are smaller than large-span arch greenhouse,and the area of extreme wind pressure is small.Therefore,its wind resistance performance is superior.When the windward side vent,leeward side vent and both side vents are opened,the M-shaped greenhouse is subjected to the superimposed effect of "upper suction and lower pressure" compared with the ordinary large-span arch greenhouse.The maximum values of average net wind pressure coefficients are-1.48 and-2.00,+0.92 and-1.68,-1.05 and-1.90,respectively.When the top vents are opened,the windward side of M-shaped greenhouse and ordinary large-span arch greenhouse form the superposition effect of "upper pressure and lower suction",and the maximum values of average net wind pressure coefficients are +1.09 and+1.71,respectively.When the windward side vent and top vents are opened,and when all the side and top vents are opened,there are no significant differences between the internal and external wind pressure coefficients of M-shaped greenhouse and ordinary large-span arch greenhouse.The maximum values of the average net wind pressure coefficients are-1.03 and-1.05,-0.51 and-0.56,respectively.For the conditions with open side vents,the average values of internal pressure coefficients estimated by theory are in good agreement with the results obtained from numerical simulation.The results meet the requirements of the relevant codes.(3)Research on the ventilation and cooling performance of M-shaped greenhouse and ordinary large-span arch greenhouseThere is no obvious vortex in both types of greenhouse when only side vents are opened,and the difference of airflow between M-shaped greenhouse and ordinary large-span arch greenhouse is small.When both side and top vents are opened,the vortex area is larger and there is small local turbulence in ordinary large-span arch greenhouse.The structural design of V-shaped area of M-shaped greenhouse changes the direction of airflow to a certain extent and break the turbulence phenomenon better.The area where the vortex is generated in the greenhouse is small and concentrates in the local area near the canopy on the windward side of the greenhouse.The overall wind speed of M-shaped greenhouse is greater than that of ordinary large-span arch greenhouse.The airflow is faster,with wind speed differences of 0.4 m/s and0.3 m/s at crop heights of 1.2 m and 1.8 m respectively.The ventilation efficiency of M-shaped greenhouse is higher and has better uniformity.Part of the airflow at the top of M-shaped greenhouse is exchanged with the low-temperature air outside the greenhouse to participate inside ventilation again,which is conducive to ventilation and cooling.The temperature inside the M-shaped greenhouse is lower than ordinary large-span arch greenhouse along the span direction.The average temperature of the horizontal section is also slightly lower.In summary,M-shaped greenhouse has significantly improved wind resistance compared with ordinary large-span arch greenhouse,and it has good ventilation and cooling effect in summer.It is suitable for promotion and application as a new type of greenhouse.The research results can promote the development of agricultural facilities and facilitate disaster prevention and mitigation.The innovations are as follows:(1)The large-span M-shaped greenhouse with superior wind resistance and cooling performance that is suitable for mechanization is proposed,and the optimal angle of the Vshaped area on the roof is obtained.(2)The multi-field coupled simulation analysis of wind,humidity and heat are realized.The wind resistance and ventilation cooling characteristics of the M-shaped greenhouse are explored.