基于SPH-FEM的油菜茎秆磨粒气体射流切割仿真与试验

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

针对传统油菜收获切割刀具振动大、茎秆缠绕磨损及效率低等问题,该研究提出一种油菜茎秆磨粒气体射流切割技术,以实现作业机具与油菜无接触式切割和高效低耗收获。采用光滑粒子流体力学与有限元(smooth particle hydrodynamic-finite element method,SPH-FEM)耦合仿真对油菜茎秆射流动态切割过程进行分析,揭示气-固间能量传递规律,获取射流切割动态特性,并搭建试验系统进行射流切割试验验证。研究结果表明,采用4 mm孔径高速喷嘴,射流压力为20 MPa时气流及磨粒最高速度分别为741和411 m/s,约95%加速过程发生在喉管段与扩张段;喷嘴外流场流速呈现先下降后上升的变化规律,射流压力越大速度变化越剧烈;射流束主要通过气体膨胀-收缩-膨胀的加速过程将压力能转化为射流束动能;入口压力从3 MPa增加至10 MPa时,磨粒最大速度提升率从31%下降至11%。当压力超过3 MPa后,随射流压力提高,射流束压力能-动能转换效率显著减小;在相同条件下0.1 mm粒径磨粒的最大速度比0.3 mm粒径磨粒大19%;粒径越大磨粒获得的切割动能越大,0.3 mm粒径磨粒切割动能最大,其次为0.2与0.1 mm粒径磨粒;磨粒速度在120 m/s时可以实现茎杆有效切割,对应射流压力约为0.4 MPa;横移速度为5 mm/s、靶距在10 mm以内可一次切断茎秆,横移速度超过5 mm/s时无法一次切断茎秆;靶距5 mm、横移速度5 mm/s时,可获得最小切割侵蚀体积,切口宽度在1~6 mm之间;射流切割能力主要受横移切割速度影响,切割靶距影响相对较小;茎秆切割效果主要受靶距影响,横移速度影响相对较小。研究成果还可用于其他类似作物茎秆的切割,可为农业非接触式高效切割技术装备的开发提供理论与技术支撑。

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 noncontact 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,O.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.