鸡体鸡笼阻挡对密闭鸡舍气流运动影响的数值研究

在建立密闭式鸡舍机械通风系统气流运动方程的基础上,推导了由流函数和势函数表示的气流运动控制方程。根据能量变分原理,导出了平面等参可变节点的统一有限元模型。重点讨论了流函数形式下的多连通域(即鸡舍内存在阻挡物)方程的数值分析法。提出了采用流场叠加法求解时的两种内边界条件确定方法:①切向循环速度为零条件:在任一封闭内边界上切向循环速度为零;②能量最小条件:真实内边界条件使整体流场的能量最小。通过上述两种条件建立了原方程的补充代数方程,使问题得到了圆满解决。运用数值模拟,比较了横向通风与纵向通风系统在舍内气流分布型式上的特点。结果表明,在纵向通风形式下,鸡舍内的气流分布非常均匀,鸡体鸡笼等障碍物对空气运动的阻挡作用不十分明显。相反,横向通风系统的气流分布极不均匀,尤其下部鸡笼周围的气流速度大大降低。

Numerical Study on Air Movement as Affected by Obstacles in a Confined Chicken House

On the basis of the establishment of air movement equations in a confined ventilated chicken house, the governing equation, represented by the stream function and potential function, is deduced. According to the principle of energy variation, a plane finite element model with variable-node isoparameter elements is then developed. Importance is attached to the numerical solution of the equation in the form of stream function for a multiply connected region (i.e. there exist obstacles such as chicken bodies and the stacked-cages. ). Two approaches to determine the inner boundary conditions are proposed while adopting the fluid region supperposition method as follows; (1)zero circular tangent velocity condition. The integration of the tangent velocity in a closed inner boundary equals to zero; (2)minimum energy condition. The actual inner boundary conditions result in the total energy of the flow region to be minimum. Based on any of the above two conditions, a supplementary algebraic equation is thus established, which makes the problem well-defined.The differences in air distributions between cross ventilation and tunnel ventilation systems are compared with and without obstacles through computer simulations. The results show that air distributes very uniformly under tunnel ventilation,and obstacles inside the building have no obvious effects on the airflow pattern. However,air distribution under cross ventilation is extremely uneven, especially air velocity under the stacked-cages decreases greatly.