Simulation and Verification of Suspension Characteristics and Throwing Airflow Velocity of Cotton Stalk Fragments with Different Moisture Contents Based on CFD-DEM

Changes in the moisture content of cotton stalks during harvest complicate the selection of airflow velocities for suspending and spreading stalk fragments. Stable suspension velocities were measured for cotton stalk fragments in four moisture-content ranges. Contact parameters were determined using cylinder-lifting, inclined-plane, and drop tests. The ability of the discrete element method (DEM) model to reproduce dynamic piling was assessed by comparing simulated and measured dynamic angles of repose in rotating-drum tests. Two-way coupled computational fluid dynamics–discrete element method (CFD–DEM) simulations were used to predict suspension velocities and investigate spreading through a curved discharge chamber. The equal-weight mean suspension velocity across the four operating conditions increased from 7.82 m/s for the 15–25% moisture-content group to 11.85 m/s for the 45–55% group. The relative errors between the CFD–DEM predictions and the corresponding experimental four-condition means ranged from 3.38% to 4.85%. At an operating airflow velocity of 1.5 times the corresponding suspension velocity, mean spreading uniformity across the four moisture-content groups reached its highest measured value of 89.96% in the bench tests. The mean relative error between simulated and measured spreading uniformity was 2.88%. These findings provide a basis for estimating the suspension velocity of cotton stalk fragments at different moisture contents and selecting the operating airflow velocity for the tested curved discharge chamber.