基于柯恩达效应的小区收获机高效除杂装置辅助板设计与机理研究

Design and Mechanism Study of Auxiliary Plate of New Hig-efficiency Impurity Removal Device for Plot Harvester Based on Coanda Effect

摘要:

在小区收获机中，基于柯恩达效应的除杂系统是一种新型二级除杂装置，具有结构简单、空间占比小的优势。在实际应用中，仅依靠曲面的柯恩达效应仅能实现杂质分离，大部分杂质无法在气流作用下有效去除，导致除杂效率较低。为提升装置的除杂效率，增强曲面末端的柯恩达效应强度，并减少气流扩散现象，本文在原有除杂装置的基础上，增设了辅助板结构。基于CFD-DEM方法，获取了无辅助板时小麦籽粒和颖壳杂质的颗粒偏转角，并利用这些颗粒偏转角，通过几何关系确定了辅助板自由端角度的变化范围为4.89°~27.12°。借助数值仿真方法，深入研究了装置内部柯恩达效应作用带的流场结构，确定了柯恩达效应末端速度突变处的高度位置范围为0.112~0.128m。基于仿真结果，进一步明确了辅助板长度及其固定端对应位置。最终，通过台架试验得出，当辅助板自由端角度为25°，长度为155mm，固定端高度位置为0.122m时，除杂效果最佳，籽粒含杂率为0.998%，充分证明了辅助板在提升除杂装置性能方面的显著作用。

Abstract:

In the plot combine harvester, the impurity removal system based on the Coanda effect serves as a novel secondary cleaning device, featuring advantages of simple structure and compact spatial footprint. However, in practical applications, relying solely on the Coanda effect generated by curved surfaces can only achieve partial impurity separation, as most impurities fail to be effectively removed under airflow, resulting in suboptimal cleaning efficiency. To enhance the device’s performance, strengthen the Coanda effect intensity at the end of the curved surface, and mitigate airflow diffusion, an auxiliary plate structure was introduced to the original design. Using the CFD-DEM method, the particle deflection angles of wheat grains and husk impurities were obtained for the configuration without the auxiliary plate. These angles were then utilized to determine the variation range of the auxiliary plate’s free-end angle (4.89°~27.12°) through geometric relationships. Numerical simulations were employed to analyze the flow field structure within the Coanda effect zone of the device, identifying the height range (0.112~0.128m) where abrupt velocity changes occurred at the end of the Coanda effect. Based on simulation results, the optimal length of the auxiliary plate and the positioning of its fixed end were further refined. Bench tests demonstrated that the highest cleaning efficiency was achieved when the auxiliary plate had a free-end angle of 25°, a length of 155mm, and a fixed-end height of 0.122m, and the impurity content in the grain is 0.998%, conclusively validating its significant role in improving device performance.