Abstract: Cotton is one of the important raw materials in the textile industry. After processing, it is used to manufacture various textile products. The presence of foreign fibers in cotton can have an impact on the quality of the finished yarn, the fabric surface effect, the performance and the subsequent process treatment. Therefore, in the textile production process, it is necessary to effectively screen, separate, or control foreign fibers in the raw materials to ensure that the quality and performance of the final products meet the expected requirements. The cotton foreign fiber sorting machine effectively separates foreign fibers and impurities through high-speed rotating brush rollers, airflow and vibration. However, there is still room for improvement in terms of foreign fiber detection rate, energy consumption, and rejection rate. As a key component in the foreign fiber sorting process, the reasonable design of the reject nozzle structure is crucial to the efficiency and accuracy of the foreign fiber sorting machine.
The nozzle is critical to ensuring fiber quality and maintaining production efficiency by providing precise positioning, efficient rejection, continuous production, and reduced human intervention during foreign fiber rejection. By applying high-pressure airflow, the nozzle can quickly and accurately remove foreign fibers from the fibers, ensuring smooth operation of the production line, improving production efficiency, and reducing production costs. Therefore, optimizing the nozzle structure to reduce energy consumption and improve rejection rate is necessary. The Laval nozzle is a specially designed nozzle commonly used in rocket engines, jet engines, and other fields that require high-speed airflow. In practical use, the Laval nozzle can accelerate the gas from subsonic to supersonic speeds, achieving the effect of gas acceleration while improving efficiency, controlling flow rate, reducing backpressure effects, avoiding equipment overheating, and simplifying the structure. Therefore, the unique shape and functionality of the Laval nozzle provide reference for the optimization design of the rejection nozzle structure.
In summary, in this study, we aim to optimize the structure of the rejection nozzle in the cotton foreign fiber sorting machine based on the characteristics of the Laval nozzle's contraction-expansion design. Numerical simulation is used to analyze the external flow field characteristics of the nozzle before and after optimization. By comparing the changes in velocity, pressure, and air consumption, the feasibility of the optimization design is validated to provide theoretical reference for the practical application of the nozzle, so as to achieve the goal of improving the performance of the whole machine by realizing the efficient removal of foreign fibers.

Key words: foreign fiber sorter, nozzle, flow field simulation, optimization design, numerical simulation

摘要： 为提高异纤分拣机剔除速率，降低能耗，基于拉瓦尔喷嘴的结构特性对异纤分拣机剔除喷嘴进行了结构优化设计。采用维托辛斯基公式对喷嘴收缩段进行优化，喷嘴喉部采用自然过渡的方式实现流线型的几何形状变化，喷嘴扩张段采用特征法进行优化。对优化前后的喷嘴结构进行数值模拟分析，监测对比优化前后喷嘴外流场的速度、压力和耗气量，评估优化设计对喷嘴外流场性能的影响。结果表明：优化后喷嘴外流场的最大速度相较于原始喷嘴速度提高25.7%，在分拣异纤的主要作用区域耗气量降低33%，同时喷嘴外流场的压强变化更加平缓，即相较于原始喷嘴，优化后的喷嘴结构能耗更低、综合性能相对更优。

关键词: 异纤分拣机, 喷嘴, 流场仿真, 优化设计, 数值模拟