Abstract. Mixing fans (MFFs) are widely used in ventilation of agricultural buildings to improve the uniformity of the air supply, thereby improving the ventilation efficiency. In order to improve the ventilation performance of MFFs, a new visor-shaped diffuser was designed and installed on a MFF. The angle and the length of the diffuser were crucial parameters that affected the performance of the MFFs with the diffusers. Thereby, in this study numerical simulation with 42 diffusers of different angles (ranged from 90-270°) and different lengths (ranged from 150-650 mm) with the MFF were studied with Computational Fluid Dynamics (CFD) simulation to acquire the optimal design of diffusers. The numerical simulation results show that the diffusers of 90°/450 mm, 120°/350 mm, and 150°/250 mm with jet lengths of up to 5.85, 5.90, and 5.85 m, respectively, had better performances among all the diffusers. The optimal prototype diffusers of 90°/450 mm, 120°/350 mm, and 150°/250 mm of MFFs were tested by laboratory study and field test. The test was conducted in wind speed distributions at distances of 0.5 to 1.0 m from the axial of MFFs. During the test, we evaluated the MFFs performance such as maximum flow flux, maximum energy efficiency, and non-uniformity coefficient. The diffuser of 150°/250 mm showed the best performance, increasing the flow flux and energy efficiency by 3.8% and 11%, respectively, and obtain higher axial wind speeds and larger non-uniformity coefficients. Finally, the diffusers of 150°/250 mm were tested in a free-stall dairy barn. The field test result shows that the diffusers of 150°/250 mm increased overall average wind speeds by 7.4% and local average wind speeds at bedding 1 and bedding 2 by 31.0% and 27.7%, respectively, which agreed with our numerical simulation and laboratory test. This optimal design of mixing fans could be applied to improve the air mixing in agricultural buildings. Keywords: Agricultural buildings, Diffuser, Mixing fan, Numerical simulation, Optimization.

Abstract.With the rapid development of modern agriculture facilities, agricultural fans have been widely used due to their low pressure and large airflow characteristics. However, existing agricultural fans have large flow losses and low energy efficiencies. To increase the airflow and energy efficiency of these fans, optimization designs based on skewed and swept blades were carried out. First, a “DDZ” agricultural fan (a leaf model agricultural fan commonly used in China) was chosen as the archetype fan. Its performance curves and flow field distribution were obtained by performance testing and numerical simulation. Second, the stack lines of the skewed blade and swept blade were designed based on the original blade, 3 skewed blade parameters (skewed angle a, x direction control parameter kx, and y direction control parameter ky), and 3 swept blade design parameters (swept angle ß, z direction control parameter kz, and r direction control parameter kr). Finally, the optimal skewed blade design parameters (a = 16.8°, kx = 1.65, and ky = 0.5) and optimal swept blade design parameters (ß = 10.6°, kz = -0.33, and kr =0.6) were obtained using numerical simulations and orthogonal testing, which is a response surface method. The numerical simulation results showed that the airflow and energy efficiency ratios of the optimal skewed blade fan were increased by 4.3% and 20.5%, and those of the optimal swept blade fan were increased by 4.5% and 15.4%, respectively, in comparison with those of the original fan. The flow fields showed that the optimal skewed blade mainly reduced the radial flow at the blade root and the leakage flow. The optimal swept blade mainly reduced the leakage flow by changing the distribution of the static pressure on the blade surfaces. Keywords: Agricultural fan, Skewed-Swept blade, Numerical simulation, Optimization.

To study the influence of ripple cross angles on the resistance of wet curtains, wet curtains with different ripple cross angles (45°/45°, 45°/15°) were tested on agricultural ventilation equipment performance testing benches, and the static pressure drop under different wind speeds (1-3 m/s) was determined. Four turbulence models (κ-ε, RNG κ-ε, κ-ω, SST κ-ω) were adopted for numerical simulations of the two types of wet curtain, and the simulations' results were compared with those of experiments. The average errors found are 41.1%, 48.7%, 27.1%, and 27.8%, respectively, and the κ-ω model is found to be the most suitable one for the calculation of wet curtain resistance among the four turbulence models. By using the κ-ω turbulence model, the static pressure drop performances of wet curtains with ripple cross angles 45°/35° and 45°/25° were calculated. Resistance increases with wind speed and ripple cross angles, and a large ripple cross angle has a higher resistance growth rate with increasing wind speed.