摘要
低屋面横向通风(low profile cross ventilated,LPCV)牛舍作为中国大型奶牛场一种新的牛舍建筑形式近年来得到了广泛应用,但实际运行中存在舍内气流分布不均匀、夏季高温高湿、冬季低温高湿等环境控制技术瓶颈。为了研究LPCV牛舍空气流场的分布规律,以指导该种牛舍的改进和优化设计,该文在现场实测的基础上,采用计算流体动力学CFD(computational fluid dynamics)方法,根据现场和实验室实测值所确定的风机、湿帘等边界条件,对LPCV牛舍的气流分布进行了三维数值模拟。模拟时将牛只按与实物原型等比例引入到模型中。模拟结果表明:挡风板和颈枷下面矮墙的设置影响了舍内气流分布的均匀性。在既有牛舍挡风板设置和矮墙高度不能改变的情况下对牛舍进行了局部改造,改造后舍内气流分布得到明显改善,平均风速增加了52.8%,气流不均匀性指标降低了41.8%。模拟值与实测值的对比表明,28个测点测试值与模拟值平均相对误差的平均值为17.1%,说明现场实测与数值模拟有较好的吻合度。该研究可为中国LPCV牛舍结构优化设计和环境调控提供参考。
The first low profile cross ventilated （LPCV） dairy cattle barn was built in fall 2005 in North Dakota. The barn is generally a fully enclosed facility characterized by a low roof pitch of 0.5/12 and a warehouse-type structure. It was introduced to China in 2009 and since that time several barns have been built in large dairy farms in China as a newly-developed dairy cattle barn type. The LPCV barn offers some of the advantages of natural ventilated and tunnel ventilated freestalls and allows producers to have some control over the cow’s environment during all seasons of the year. But in China there are technical bottlenecks for environmental control problems in operation, including uneven distribution of indoor airflow, high-temperature and high-humidity in summer, low-temperature and high-humidity in winter et al. The use of computational fluid dynamics （CFD） techniques to solve complex fluid problems has greatly increased in recent years. In this study, a full-scale dairy cattle house was modelled to investigate the distribution pattern of airflow in LPCV barn. The simulation of dairy cattle was considered to improve the reliability of the CFD model, as the presence of cows in barns can significantly influence air flow patterns and internal environmental conditions. The evaporative cooling pads on the air intake side of the barn were considered as porous media and the coefficients of the viscous and inertial resistances were determined by laboratory values. The performance curve of the exhaust fans on the air outtake side was measured in laboratory to establish the boundary conditions of the fans. Baffles are located over stalls in LPCV barn to increase air velocity in each freestall area. Simulation results shows that the problem of uneven flow distribution is generally exist in the barn. The wind speed differed greatly between the two sides of the baffle in the bedding area. The wind speed was significantly lower for the windward side compared with the other side. The main reason for the uneven flow distribution in the barn was the parapet below the neck rails. If there is no parapet, the average wind speed could increase by 60.6%, and the air uniformity coefficient could decrease by 68.7%. For the existing LPCV barn, keeping the baffle wall and the parapet unchanged, the air flow could be improved by the installation of a baffle on top of the neck rails of the windward of the feeding alley. The modification has a significant effect on the airflow distribution improvement, with the averaged wind velocity increased by 52.8%, the airflow uniformity coefficient decreased by 41.8%. The CFD model was validated via comparison with the field experimental results at the same locations where the sensors were installed. Comparison between simulations and measurements showed that the average relative error of the test and simulated value for the 28 test points was 17.1%, which indicates that there is a goodness of fit between field measurement and numerical simulation. And this study can provide references for the optimization design and environment regulation of LPCV dairy cattle barn in China.
出处
《农业工程学报》
EI
CAS
CSCD
北大核心
2014年第6期139-146,共8页
Transactions of the Chinese Society of Agricultural Engineering
基金
公益性行业(农业)科研专项资助项目(201303091)
国家奶牛产业技术体系资助项目(CARS-37)
中央高校基本科研业务费专项资金资助(2012YJ015)
关键词
计算流体动力学
流场
模型
低屋面横向通风
奶牛舍
数值模拟
computational fluid dynamics
flow fields
models
low profile cross ventilated
dairy cattle barns
numerical simulation
