Investigation of the burial and mixing performance of a rotary tiller using discrete element method

Rotary tiller is a widely used tillage tool in China, and its burial and mixing ability determine its performance. Discrete element method (DEM) is a promising numerical method to study the soil-tool interaction, and a suitable contact model is required to obtain a reasonable accuracy. In order to investigate the burial and mixing performance of a rotary tiller consisted of rotary blade and spiral horizontal blade in silty clay loam, two cohesion contact models HM-B and HM-JKR were compared. The sensitivity analysis for HM-B and HM-JKR were conducted by Plackett-Burman test. The bonding stiffness of HM-B and the surface energy of HM-JKR were the most sensitive parameters for their contact model, respectively, and were calibrated to compare their simulation performance. HM-JKR obtained a relatively smaller error on torque compared with measurement results in a soil bin test. The tillage characteristics of rotary blade and spiral horizontal blade were studied, and the effect of working conditions and rotary tiller structures on these were investigated by simulation. The distribution ratio and the disturbance intensity were selected to evaluate the burial and mixing performance. Compared with rotary blade, the spiral horizontal blade obtained a larger disturbance area and intensity. Tillage depth had the most significant effect on the tillage characteristics. The average disturbance intensity of rotary blade and spiral horizontal blade increased nearly 25% and 30% with the increase of tillage depth from 150 mm to 180 mm. The L-bend structure of the rotary blade was important to the burial and mixing performance of rotary tiller. A reasonable number of rotary blade group in the rotary tiller and distance between each rotary blade group can obtain a satisfied burial and mixing performance with a relative low torque consumption.