CFD-DEM simulation and performance analysis of a constructed alfalfa leaf collector

This study evaluated the performance of a pneumatic collection system designed to reduce losses of nutrient-rich alfalfa leaf fractions during harvesting. The system consisted of a suction unit integrated with a cyclone separator. A coupled computational fluid dynamics–discrete element method (CFD–DEM) framework was employed to systematically investigate the effects of key operating parameters, including airflow velocity (9, 13.5, and 18 m s -1 ), machine forward speed (2, 3, and 4 km h -1 ), and soil particle diameter (0.2, 1.0, and 2.4 mm). Additional simulations were conducted to assess the impact of cyclone design modifications, including a twofold increase in suction pipe radius, a 50% reduction in cyclone diameter, and the incorporation of a vortex finder. The results showed that an airflow velocity of 9 m s -1 resulted in the accumulation of soil particles and alfalfa leaves at the cyclone inlet, causing partial blockage of the suction pipe. Increasing the airflow velocity substantially improved leaf collection and separation efficiency; however, it also promoted greater soil entrainment, thereby decreasing the purity of the collected material. Higher machine forward speeds reduced leaf collection efficiency because the shorter residence time of leaves within the suction zone limited their entrainment into the airflow stream. Reducing the suction pipe cross-sectional area effectively prevented inlet blockages and enhanced overall system performance without increasing fan power requirements. Although the inclusion of a vortex finder improved leaf–soil separation, complete separation was not achieved due to the similar terminal velocities of small alfalfa leaves and fine soil particles. Consequently, a fraction of the material remained suspended or retained within the cyclone, reducing separation effectiveness.