Abstract:

Objective Rotor spinning belongs to airflow spinning, the airflow in each spinning machine affects the movement of the fiber. The study and comparison of the accuracy and difference of the airflow field can provide reference for the improvement of the spinning mechanism, so as to improve the yarn quality. To investigate the accuracy and differences of airflow field produced in combing and trash removal zone of rotor spinning simulated by two-dimensional (2-D) and three-dimensional (3-D) model, the numerical simulation results of 3-D model is compared to that of 2-D model. It is expected to express the suitable application of numerical simulation in guidance of structure and parameters modification in rotor spinning.

Method COMSOL simulation software was used to build the 2-D and 3-D geometric models of the combing and trash removal area. The model included combing chamber, sliver entrance, debris removal area and fiber transport channel. Model Ⅰ was a 2-D model, and Model Ⅱ and Ⅲ were 3-D models with different wedge shape of fiber transport channel. The "frozen rotor" in COMSOL multiphysics simulation was a special "steady-state" study dedicated to calculation of the velocity, pressure, and turbulence fields of flow in rotating machinery. The rotation was analyzed by introducing centrifugal forces.

Results The numerical simulation results of 2-D and 3-D models were similar in general, but differed in some results. The velocity at the exit of the fiber transport channel of 3-D model was higher than that of 2-D model, therefore, velocity distribution of 3-D model indicated a better improvement of fiber straightness. The energy of the turbulent flow in the 2-D model was basically below 10 J. The airflow is relatively stable, and only two large turbulent flow were generated near the entrance wall. In Model II, the turbulent flow was floated at the air filler due to a vortex, but it gradually became smaller as the cross section of the fiber transport channel got smaller, and the airflow was slowly stablized. The airflow stability in Model Ⅲ was obviously poor with many vortices, and the turbulent flow changed greatly. The velocity, pressure and turbulent energy distribution associated with the 3-D model was slightly more uniform than that of 2-D model, and the airflow and turbulent energy distribution in the trash removal area with the 3-D model was more accurate than that of 2-D model.

Conclusion The variation in velocity and pressure gradient at the outlet of the fiber transport channel of 3-D model is significantly larger than that of 2-D model. The airflow velocity, pressure and turbulent kinetic energy distribution in the lower half of the carding chamber of 3-D model is more uniform than that of 2-D model. The turbulent kinetic energy at the junction of the carding chamber and the debris removal area of three models illustrated large fluctuations due to intersection of airflow, but the airflow direction distribution demonstrated by 2-D model is not conducive to the exclusion of impurities with small volume and mass. Although there is a low-speed vortex in the trash removal area of 3-D model, there is airflow to the trash removal port, which is conducive to the exclusion of impurities. The wedge symmetric Model II has a slightly higher exit velocity maximum in the fiber transport channel than Model III, and the gradient change of pressure is more obvious and the turbulent kinetic energy change area is small. The movement of impurity particles in the 3-D models are better than that in the 2-D model, most of the impurity particles will be eliminated in time with the movement of the airflow, and only a small portion of the impurities will enter the fiber transport channel. Therefore, the geometric structure of wedge symmetric 3-D model II has better carding and separating effect on fiber bundles, which is beneficial to transfer of single fibers and straightening of hooked fibers. By comparison, the 2-D model simulation lacks accuracy besides small computational time and easy operation. The simulation results of the 3-D model are better than those of the 2-D model, and the 3-D model can show the numerical results on different levels, and the simulation of the details of the flow field and particle distribution is more accurate and intuitive, which is suitable for guiding the actual production and optimising the design of the rotor spinning mechanism.

Key words: rotor spinning, carding and trash removal, numerical simulation, airflow field, three-dimensional model, two-dimensional model