Simulation and experiments of abrasive gas jet cutting for rapeseed stem using SPH-FEM

Rapeseed harvest cutting tools have been confined to large vibrations, entanglement, wear, and low efficiency. In this study, gas jet cutting was proposed for rapeseed stems using abrasive particles. This technique aimed to achieve the non-contact cutting between the machinery and the rapeseed, thereby ensuring efficient and low-consumption harvesting of rapeseed. The dynamic jet cutting of rapeseed stems was simulated using the smooth particle hydrodynamics-finite element method (SPH-FEM). The energy transfer between gas and solid phases was obtained for the dynamic behavior of the jet cutting. A test system was constructed to experimentally verify the jet cutting. The research results indicate that the maximum speeds of the airflow and abrasive particles were 741 and 411 m/s, respectively, when using a high-speed nozzle with a 4 mm diameter at a jet pressure of 20 MPa. Approximately 95% of the acceleration occurred in the throat and expansion sections. The external flow field of the nozzle exhibited a fluctuating pattern with the first decreasing and then increasing. The greater the jet pressure was, the more pronounced the velocity contraction and expansion fluctuations were. The jet beam primarily accelerated during gas expansion-contraction-expansion, thus converting the pressure into the kinetic energy of the jet beam. Once the inlet pressure increased from 3-10 MPa, the acceleration efficiency of the abrasive particles decreased from 31% to 11%. When the pressure exceeded 3 MPa, there was a further increase in the jet pressure, leading to a significant reduction in the efficiency of converting jet beam pressure energy to kinetic energy. At the same time, the maximum speed of abrasive particles with a diameter of 0.1 mm was 19% higher than that with a diameter of 0.3 mm. The larger the diameter of the abrasive particles were, the greater the cutting kinetic energy they obtained. Among them, 0.3 mm diameter abrasive particles exhibited the highest cutting kinetic energy, followed by 0.2 mm, and then 0.1 mm diameter. The minimum jet pressure of 0.4 MPa was required for the cutting rapeseed stems, with a lateral movement speed of 5 mm/s. Therefore, the stem was cut through in a single pass at a target distance of 10 mm. Once the lateral movement speed exceeded 5 mm/s, there was no cutting through in a single pass. When the jet nozzle was positioned 5 mm away from the target and the lateral movement speed was 5 mm/s, the minimum volume of cutting erosion was achieved in the incision widths ranging from 1 to 6 mm. The findings can also be applied to the cutting of similar crop stems. Theoretical and technical support can also be offered for the non-contact high-efficiency cutting equipment in modern agriculture.