| Popis: |
One of the most significant and persistent environmental concerns regarding swine production is the transport of odor constituents, trace gases, and particulates from animal production and manure storage facilities. The objectives of this study were to determine how swine housing unit orientation affects air velocity and turbulence and to assess the opportunities for reducing off-site transport of air quality constituents from manure storage facilities located downstream from confinement buildings. Measurements were made with 1:300 models of swine finisher buildings in a low-speed wind tunnel capable of producing air velocities up to 12 m s-1 (27 mph). Runs were completed with no building models, with one housing unit oriented parallel and perpendicular to airflow, and with four housing units oriented parallel, perpendicular, and at a 30° angle to airflow. Velocity and turbulence measurements were completed in a grid of 83 points within a 215 mm high × 400 mm wide (8.5 × 15.7 in.) vertical plane at separation distances 2H, 5H, and 10H downstream from the building model arrays (H = model height of 17.5 mm) using a constant temperature anemometer system with a 3-D hot-film probe. A large zone of reduced longitudinal velocity (u) and increased turbulence intensity (Iu) in the wake of model buildings oriented perpendicular to flow was observed and was still apparent 10H downstream. The size and strength of this turbulent wake is attributed to the sloping roofs of the building models that, with a frontal vortex under the upwind building eave, create an unexpectedly tall wake zone in the building lee. One or four parallel building model arrays exhibited the least influence on downstream velocities and turbulence intensities. One perpendicular and four 30° models produced intermediate effects. The observed reduction in air velocity up to 10H downstream from multiple buildings oriented perpendicular to the airflow suggests that entrainment and transport of air quality constituents from manure storage structures may be reduced when these structures are located in this zone. However, increased turbulence in the wake zone and field conditions with variable wind speed and direction and atmospheric stability may counter the effects of reduced velocity. Tracer studies, either in wind tunnel experiments or in the field, are needed to verify the potential for building orientation and spacing to reduce transport of air quality constituents from manure storage structures. |
