The CFD Simulation And Improvements Of Ventilation In Stacked-cage Laying Hen Housing

The environment could significantly affect the healthy condition and production performance of laying hens.In the high density stacked-cage laying hen housing,the poor airflow condition in caged-hen occupied zone(CZ),uneven airflow distribution and low ventilation efficiency are common existed issues.This study researched the generation method of airflow resistance calculation model of hen flocks and airflow distribution simulation model in the hen house with tunnel ventilation by means of computational fluid dynamics(CFD).Meanwhile,the effect of cage height in stacked-cage hen house,the installation of deflectors under ceiling and the effect of air supply location on the airflow speed and distribution in laying hen housing were also investigated.The results are as following:1.On account of the airflow resistance of caged-hen flocks,the virtual wind tunnel was adopted to research the effect of geometric model simplification method,volume of hen and the flock distribution on airflow resistance,the study built a hen simplified model that ignored the beak,crown and leg and the airflow resistance calculation model of flocks.The model was validated by comparing the measured with simulated values and the relative error was less than 6%.This study gave a method concerning airflow resistance coefficient calculation of hen flock,which included the geometric model building of virtual wind tunnel,the establishment of numerical simulation method and boundary conditions.This study laid a foundation of airflow simulation in stacked-cage hen housing.2.On account of effect of the cage height on airflow speed in cage,this study built a ventilation simulation model of stacked-cage laying hen housing,which included the establishment of geometric model of hen house,the numerical methods and boundary conditions in the simulation.And researched the airflow speed in cage under different heights of free space above the CZ(0.15 m,0.3 m,0.45 m,0.6 m and 1 m)with CFD simulation.The results showed that,the average speed of the free space above CZ was positive correlated with the height.When the average airflow speed of the cross profile of poultry housing was 1.5 m s-1,the regression relationship between the speed of space above CZ and the height is:Y=0.1681n(x)+1.22."Y" is the speed in free space above CZ,m s-1;"x" is the height of free space above CZ,m.The environment simulation model and boundary condition model were validated by the field experiment,the relative difference between simulated and measured values was less than 10%,which could provide theoretical basis for the improvement of facilities in stacked-cage poultry housing.3.In order to improve the ventilation efficiency of tunnel ventilation and the cooling effect of hens.This study simulated the effect of deflectors with varied heights(the space between the bottom of deflectors and the top of cage were 0.4 m,0.55 m,0.7 m,0.85 m and 1.0 m,respectively)and varied intervals(6 m,9 m,12 m,15 m and 18 m)on airflow speed and distribution in hen house.The result showed that the speed in aisle was linearly related with the height and interval of deflectors,when the average velocity of cross profile of poultry housing was 2.3 m s-1,the multiple regression relationship between the air speed in aisle and height as well as interval of deflectors was:Y=0.50h-0.02d+2.662(Pa<0.01,Pb<0.01),"Y" is the average speed in aisle,m s-1;"h" is the height of deflector,m;"d" is the interval of deflectors,m.The airflow distribution uniformity in CZ was positively related with the height of deflectors,and negatively related with intervals.The speed variation trend along the length direction of cage was similar under different heights while was significantly different under varied intervals.4.Researched the effect of air supply location and flaps rear the inlet on airflow in cage with CFD simulation.The result showed that when there is no flaps rear the cooling pad,the increase of distance between air supply location and cage could decrease the ventilation weak zone and dead zone in cage near the inlet.It is necessary to make full use of the gable wall when installing the cooling pad.The flaps could increase the vortex and weak zone neat the inlet,which could decrease the airflow distribution uniformity in cage near the inlet.