基于鹅舍气流场CFD模拟的通风系统结构优化与验证

针对鹅舍内机械通风时大量气流扩散于鹅舍上方而位于地面鹅只通风效果受阻的气流问题,提出一种基于计算流体力学(computational fluid dynamics,CFD)的结构优化方案。通过在舍内主梁下端安装相同高度且与气流方向呈一定倾角的多个可拉伸卷膜构造方法,提高种鹅舍内有效的通风效率。依据试验现场边界条件,构建并求解了鹅舍的三维稳态模型,舍内40个测点的风速模拟值与实测值均方根误差为0.152 m/s,最大绝对误差为0.29 m/s,平均相对误差为2.04%,验证了建立的鹅舍CFD模型的准确性。根据不同优化方案数值模拟了27组不同改造后鹅舍内气流场分布情况,仿真得出最优组合方案:在42 m长的舍内安装卷膜个数为10个,卷膜与主梁竖直方向倾斜角度为60o以及卷膜最大下拉高度为1.2 m时舍内通风效率最高、气流分布最均匀。通过现场实测,对比改造前后40个测点的风速值,试验结果表明:改造后鹅舍较常规鹅舍平均风速增加0.527 m/s,舍内气流不均匀系数降低32.2%。该试验结果为种鹅舍的结构设计、同类型畜禽舍结构优化以及改善通风降温效果调控提供了一定的参考依据。

Structure optimization and validation of goose house ventilation system based on airflow field simulation by CFD

Goose is seasonal breeding animal,the goslings and adult geese supply show seasonal changes,so that the sale price of the geese is fluctuating.The out-of-season breeding technology was employed to balance annual goose production and achieve higher economic benefits by regulating the normal breeding of geese in the spring and summer of non-breeding season.This technique has been popularized in the last few years,however,the high temperature in the summer is adverse to the goose production in the process of out-of-season breeding.It is known that the quality of thermal environment and the concentration of harmful gases are important factors to the health of livestock.In order to reduce or eliminate adverse effects of heat stress and lack of water on the geese during the process of out-of-season breeding,the ventilation-cooling mode with fans and evaporative pad was employed in conventional goose house,while a large amount of airflow diffusion located in the upper part of the goose house due to that these airflow of small density flowed upward.The use of computational fluid dynamics (CFD) techniques to solve complex fluid problems has greatly increased in the last few years.In this study,the goose house with mechanical ventilation had a large number of airflow diffusion in the upper part of the goose house,this may cause a problem that the ventilation effect of the ground geese was obstructed.So a structure optimization scheme based on computational fluid dynamics (CFD) has been proposed,multiple stretching film structures were installed below the girders of goose house to change the airflow directions as well as to increase the airflow flux in the lower part of goose house around the geese.Based on that,the two factors of vertical angle between stretching film and girder,drop height of stretching film were investigated to obtain uniform airflow and higher ventilation efficiency in the goose house.A three-dimensional steady goose house model was developed by the field measured boundary conditions data.Comparison between simulations and measurements for the 40 test points of wind speed showed that the RMSE,maximum absolute error and average relative error was 0.152 m/s,0.29 m/s and 2.04％,respectively.It proved that the CFD method is reliable to estimate the distribution of air velocity in the goose house.The validated CFD model was then used to get the optimal combination scheme of 27 different construction cases:In the 42-meter-long goose house,we find that when 10 roll films are installed in the shed,and the angle between roll film and the vertical direction of girder is 60° with maximum drop height of 1.2 meters,the ventilation in the shed has the highest efficiency and its air distribution is more homogeneous,and this simulation is concluded to be the optimal one.Through in-situ test,40 points are compared before and after the transformation of the wind speed value,the average airflow velocity at the height of 0.5 meters above the ground is up to 1.01 m/s,and the average airflow velocity in the conventional goose house without film is only 0.483 m/s.The test results show that:after transforming averaged wind velocity increased by 0.527 m/s,and the airflow uniformity coefficient decreased by 32.2％,the structure of the film increases the airflow velocity in the lower position significantly.The results of this experiment provide a reference for structure optimization of similar poultry house,the internal environment regulation and the structure design of goose house.