Agricultural products are a primary source of bio-particles, which vary in shape, size, density, an‎d other physical an‎d mechanical properties. In wheat harvesting, the three main components collected from the plant are the grain, straw, an‎d chaff. The harvested material may also contain other elements such as weed seeds, soil particles, an‎d plant tissues other than the main crop. Three key performance indices in eva‎luating combine harvesters for separating grain from material other than grain (MOG) are cleanliness ratio, loss ratio, an‎d efficiency. Today, the improvement an‎d optimization of cleaning systems have become a critical deman‎d in the agricultural machinery industry. The Discrete Element Method (DEM) is a widely used an‎d powerful numerical simulation technique for modeling an‎d predicting the flow behavior of particulate materials based on Newtonian mechanics. In parallel, Computational Fluid Dynamics (CFD) models are employed to analyze fluid flow characteristics an‎d predict aerodynamic behavior. The rotary cylindrical sieve, with its simple cylindrical structure, has relatively simple construction, low weight, minimal vibration, easy operation, an‎d lower energy consumption compared to other separation systems. It is widely used in screening an‎d grading operations. This study employed CFD-DEM coupled numerical simulation to gain a better understan‎ding of microscale phenomena during the grain separation process an‎d to investigate the effects of design parameters—including airflow velocity, sieve inclination angle, an‎d sieve rotational speed—on the performance indices of the rotary cylindrical sieve. A rotary cylindrical sieve was designed an‎d constructed to validate the simulation results. Based on the size of the harvested wheat components, the sieve aperture spacing, aperture diameter, sieve length, an‎d sieve diameter were set to 3 mm, 11 mm, 700 mm, an‎d 300 mm, respectively. To simulate the cleaning system, the geometry of the sieve an‎d airflow domain was created using the SpaceClaim environment in ANSYS Workbench. The geometry was then transferred to ANSYS Meshing to generate the computational grid an‎d apply boundary conditions appropriate to the airflow physics. Following the discretization of the fluid domain an‎d the selec‎tion of an appropriate mesh size, the model was exported to ANSYS Fluent for CFD simulation. The Rocky DEM software was used to simulate particles within the cleaning system. Three-dimensional scans were used to model the wheat grain an‎d chaff particles, while straw particles were modeled as straight fibers. The physical an‎d mechanical properties of the sieve, air inlet duct, wheat grains, straw, an‎d chaff were defined accordingly. Based on variations in the loss rate, a time step of 0.00045 seconds was selec‎ted for the solution. The coupling of CFD an‎d DEM simulations was carried out within ANSYS Workbench. After simulation, validation experiments were conducted using threshed wheat with mass percentages an‎d physical characteristics matching those used in the simulation. The results indicated that airflow velocity had a significant effect on all three performance indices: cleanliness ratio, loss ratio, an‎d efficiency. The sieve inclination angle significantly affected cleanliness ratio, while the sieve rotational speed had a significant effect on both cleanliness ratio an‎d efficiency. By comparing the experimental data with the simulation results, the mean percentage error was found to be less than 5% for cleanliness ratio an‎d efficiency, an‎d 7.69% for loss ratio. To achieve maximum cleanliness ratio (85.45%), maximum efficiency (86.87%), an‎d minimum loss ratio (1.91%), the optimal parameters were determined to be a sieve inclination of 3.9 degrees, airflow velocity of 18.4 m/s, an‎d sieve rotational speed of 22.3 rpm.

مهرنوش جعفري

مهدي نادري‌نژاد

مرتضي صادقي , محمد شايان‌نژاد