Study on the air resistance of pigs in groups based on open-source CFD code: Influence of stocking density and live weight

Abstract

Animal stocking density (STKD) and live weight (LIVW) are the main factors determining the air resistance in ventilation system. To study the impact of LIVW (30, 45, 60, 75, 90, 105, 120 and 135 kg) and STKD (0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 2.0, and 2.6 pig m −2 ) on air resistance of pig groups, an open-source computational fluid dynamics (CFD) code, OpenFOAM, was adopted. Firstly, pressure drop of tube bundles which included 15 staggered tubes with a diameter of 0.40 m, equivalent to pig groups with 50-kg and 0.9 pig m −2 , were simulated for the accuracy of CFD models which were then used for calculating pig groups' air resistance for horizontal (HD) and vertical (VD) airflow directions. The validation of CFD models was based on semi-empirical equations for the tube bundle. The results indicated that: 1) The CFD model (realisable k-ε model, 10 boundary layers with 0.04 m total thickness) was reliable for pressure drop of complex bluff bodies with an average relative error of 6.80%. 2) The pig groups' friction factor for HD or VD almost increased with the rising STKD or LIVW, and regression equations were established to estimate friction factors according to LIVW and STKD of pig groups. 3) Regarding to pig groups’ air resistance, STKD is much more important than LIVW for VD, but LIVW and STKD have almost the same importance for HD. The interaction of LIVW and STKD for HD and VD has little effect. • OpenFOAM was reliable to calculate the pressure drop of complex bluff bodies. • Varied mass and stocking densities affect the air resistance of pig groups. • Pig groups' friction factors can be predicted by exponential regression equations.