Reliable estimation of the ventilation rate(VR)in intensive livestock buildings is necessary for studying building environmental control strategies and predicting indoor air quality and air emissions.As direct air exc...Reliable estimation of the ventilation rate(VR)in intensive livestock buildings is necessary for studying building environmental control strategies and predicting indoor air quality and air emissions.As direct air exchange measurements are time-consuming and expensive,it is environmentally inefficient to measure livestock building VR continuously in practice.Hence,indirect VR estimation methods have been widely used in modelling environmental control and air emissions,and also to measure airflow in the field.The accuracy of indirect measurement methods needs to be evaluated by comparing with direct measurements.In this study,the direct and indirect methods of determining hourly and daily mean VRs were applied to a mechanically-ventilated dairy free stall barn monitored by the 24-month National Air Emissions Monitoring Study.The direct method was used to continuously monitor fan rotational speeds,and differential static pressures,coupled with periodic in-situ fan performance assessments,to calculate the VR.The indirect method consisted of estimating the VR using CO2 concentration measurements and the CO2 mass balance method.The average daily and hourly means(mean±SD)of directly measured barn ventilation rates for two years were(246±73)m3/s and(245±77)m3/s,respectively.The average daily and hourly means(mean±SD)of barn ventilation rates estimated by the CO2 mass balance method were(287±93.4)m3/s and(287±118)m3/s,respectively.Correlation analyses showed a strong correlation between the indirect CO2 mass balance method and direct measurement methods(r=0.93 for daily means and r=0.85 for hourly means).展开更多
通过在三角翼上游加入干扰圆柱的风洞实验方法，研究了来流干扰对微小型飞行器MAV（Micro Air Vehicle）气动特性的影响．结果表明，在刚性和弹性三角翼顶点上游加入圆柱干扰时，两者均出现缓失速，刚性翼产生缓失速与干扰圆柱尾流关系...通过在三角翼上游加入干扰圆柱的风洞实验方法，研究了来流干扰对微小型飞行器MAV（Micro Air Vehicle）气动特性的影响．结果表明，在刚性和弹性三角翼顶点上游加入圆柱干扰时，两者均出现缓失速，刚性翼产生缓失速与干扰圆柱尾流关系密切，弹性翼的缓失速不仅与此有关，还与弹性翼的振动有关．无干扰或在机翼顶点加入干扰时，在攻角为4^o～18^o内弹性翼的升力系数比刚性翼的要大，但升阻比相对要小．由于弹性翼的振动与机翼绕流结构、气动力之间的耦合，弹性翼顶点与翼尖振动的主频随着攻角增大呈规律性的变化，失速攻角附近翼尖的振动主频是其涡脱落频率．展开更多
文摘Reliable estimation of the ventilation rate(VR)in intensive livestock buildings is necessary for studying building environmental control strategies and predicting indoor air quality and air emissions.As direct air exchange measurements are time-consuming and expensive,it is environmentally inefficient to measure livestock building VR continuously in practice.Hence,indirect VR estimation methods have been widely used in modelling environmental control and air emissions,and also to measure airflow in the field.The accuracy of indirect measurement methods needs to be evaluated by comparing with direct measurements.In this study,the direct and indirect methods of determining hourly and daily mean VRs were applied to a mechanically-ventilated dairy free stall barn monitored by the 24-month National Air Emissions Monitoring Study.The direct method was used to continuously monitor fan rotational speeds,and differential static pressures,coupled with periodic in-situ fan performance assessments,to calculate the VR.The indirect method consisted of estimating the VR using CO2 concentration measurements and the CO2 mass balance method.The average daily and hourly means(mean±SD)of directly measured barn ventilation rates for two years were(246±73)m3/s and(245±77)m3/s,respectively.The average daily and hourly means(mean±SD)of barn ventilation rates estimated by the CO2 mass balance method were(287±93.4)m3/s and(287±118)m3/s,respectively.Correlation analyses showed a strong correlation between the indirect CO2 mass balance method and direct measurement methods(r=0.93 for daily means and r=0.85 for hourly means).
文摘通过在三角翼上游加入干扰圆柱的风洞实验方法，研究了来流干扰对微小型飞行器MAV（Micro Air Vehicle）气动特性的影响．结果表明，在刚性和弹性三角翼顶点上游加入圆柱干扰时，两者均出现缓失速，刚性翼产生缓失速与干扰圆柱尾流关系密切，弹性翼的缓失速不仅与此有关，还与弹性翼的振动有关．无干扰或在机翼顶点加入干扰时，在攻角为4^o～18^o内弹性翼的升力系数比刚性翼的要大，但升阻比相对要小．由于弹性翼的振动与机翼绕流结构、气动力之间的耦合，弹性翼顶点与翼尖振动的主频随着攻角增大呈规律性的变化，失速攻角附近翼尖的振动主频是其涡脱落频率．
