夏季肉牛舍湿帘风机纵向通风系统的环境CFD模拟

为了研究湿帘风机纵向通风系统应用于肉牛舍的夏季降温效果,该试验在现场环境指标实测的基础上,采用计算流体力学(computational fluid dynamics,CFD)的方法对湿帘风机纵向通风肉牛舍的气流场与温度场进行模拟,并对系统进行改进与优化.模拟时将牛只按与实物原型等比例引入到模型中,结果表明:舍内温度分布均匀,但受牛体挡风的影响,气流分布不均,高风速区主要集中在屋顶及饲喂走道,可达0.9～1.2 m/s;牛活动区域风速较小,均小于0.6 m/s,不能满足饲养标准.在75个风速测定点剔除异常值后,气流场的相对误差范围为0.16％～94.41％,平均相对误差为34.53％,45个温度测点的相对误差范围为0.09％～10.74％,平均相对误差4.71％.通过温度场吻合性结果确定模拟与实测有较好的吻合度.在不改变牛舍围护结构及舍内构造的前提下,对牛舍进行优化,舍内安装导流板,使得温度与气流场的分布均匀性显著提高,降温效果更为显著.该研究可为湿帘风机牛舍的优化设计和环境调控提供参考.

Numerical simulation of environmental conditions for fan-pad evaporative cooling system of beef cattle barn in summer

Although fan-pad tunnel ventilation evaporative cooling system is energy efficient and environmental friendly,which consists of a fan on one sidewall and a pad on the other sidewall,is rarely applied in beef cattle barn.The cooling efficiency of the fan-pad evaporative system can reach more than 85％.With the advent of the computer age,computational fluid dynamics (CFD) technology is widely used to predict the movement of air or other environmental factors.In order to study the effects of fan-pad evaporative cooling system applied in beef cattle barn in summer,the CFD technique was used to simulate airflow and temperature distribution inside the barn,based on the environmental index measurement,to improve and optimize the effect of the system.The barn building was 54 m long,12 m wide and 4.2 m at height,window sill height was 1.5 m,and electric curtain was 2.7 m high.There were 58 beef cattle averaged 500 kg of weight included in the study.In the simulation,the beef cattle were introduced into the model according to equal proportion,a realizable k-ε model was built,and the SIMPLE (semi-implicit method for pressure linked equation) was used for the pressure velocity coupling.Measurements experiments were implemented from July to August,2014.Seventy-five measurement points were dispersed uniformly in the building at 3 different heights as 0.6,1.2 and 1.8 m above the bed floor,which respectively represented the lying down area,activity area and head above.For each measurement point,both air velocities and temperatures were recorded,using a three-dimensional anemometer and a temperature and humidity instrument respectively.Measurements were conducted at 10:00,14:00 and 18:00.These measurement indices were used for the validation of the anastomosis.Meanwhile,the velocity and the temperature of fan and pad were also measured.The temperatures of walls,floors and ceiling were recorded by thermal infrared imager (Fluke Ti400),which were used for modeling.After the simulation was completed,the results showed that the temperature distribution was uniform,but affected by the beef cattle in the barn,and the air distribution was uneven,the high air velocity area was mainly concentrated in the roof and feeding aisle with 0.9-1.2 m/s,and the wind speed of beef cattle activity area was less than 0.6 m/s,which could not meet the feeding standards.The CFD model was validated via comparison with the field experimental results at the same locations by the sensors.Comparison between simulations and measurements showed that the relative errors were 0.16％-94.41％ after 5 outlier elimination,the average relative errors were 34.53％.For the 45 temperature measuring points,the relative errors were 0.09％-10.74％,the average relative error was 4.71％,which indicated that there was a good fit between field measurement and numerical simulation.Without changing the envelope and indoor barn structure,a guide plate was arranged inside,making the uniformity of the temperature and airflow field in the room improved significantly and the cooling effects more significant.Therefore,this study can provide references for the optimization design and environment regulation of fan-pad evaporative cooling system of beef cattle barn.