| Many processing methods in the textile field are realized by redistributing,arranging and twisting fibers,based on the separation and condensation of fibers through airflow,and the coupling between the fibers and the airflow has become a common problem to be solved in gas application in the textile field.Due to the complex and changeable interaction between fibers and airflow,the research progress of gas-solid coupling mechanism is slow,and the application of airflow in the textile field still lacks basic research.Research work of this article is based on vortex spinning nozzle as the research object,three-dimensional models of nozzle and fiber were established,in addition,fiber/airflow/wall system contact model was built,the transient flow characteristics of the airflow field and the dynamic evolution of a single free-end fiber were studied under the action of coupling of high speed of airflow and fiber,the kinematics and dynamics characteristics of fiber motion with high-speed swirling airflow in three-dimensional space are theoretically expounded.The study of airflow/fiber coupling is helpful to guide the textile processing with airflow reasonably and effectively,optimize the product quality and expand the new technology.In this paper,fiber/airlow coupling was studied by numerical simulation.The research work of this paper is different from the previous studies in two aspects:(1)The airflow characteristics of unsteady and compressible airflow in the presence of fiber(bundle)were further studied;the computational burden and multi-boundary were taken into account,the dynamic grid technology was adopted for simulation.In addition,the influence of temperature,viscosity,turbulence and other factors were considered in the energy equation: this is because the high-speed airflow in vortex spinning nozzle is a turbulent flow;in addition,there will be an interaction between the airflow and the nozzle inner wall surface,that is,the viscosity of the airflow cannot be ignored;the temperature in the airflow field may affect the stiffness of the fiber and thus its motion.Therefore,a comprehensive consideration of these factors will make the simulation and prediction results of the airflow field more in line with the reality.However,the predecessors mainly focused on the airflow characteristics without fiber(bundle)in the normal spinning process,assumed that the airflow was stationary,and ignored the influence of temperature and viscosity.(2)The existing 3D fiber model was improved,and the six-dof calculation model was used for the fiber model.The contact model of fiber/air/wall system was established,and the force equation of fiber/air /wall was established by combining contact mechanics and friction mechanics.The second order nonlinear double asymptotic method was used to obtain the kinematics and dynamics equations of the fiber/air coupling action;this method is a full field solution,considering not only the compressibility of the airflow field,but also the motion nonlinearity of the fiber.Mixed tetrahedrons and hexahedrons were used to divided the grids,and dynamic meshing technology were used to simulate the motion of a single fiber with free-end under the action of high-speed swirling airflow.The main research contents of this paper are as follows:(1)study on formation mechanism of high-speed swirling airflow and airflow movement ruleIn chapter 2,the distribution characteristics of the airflow field when the machine started,including the initial state of yarn drawing-in process and the normal stable process,were simulated and studied,and the effect of airflow on spinning effect was preliminarily predicted.With the help of spinning experiment and scanning electron microscope,the strength and structure of vortex viscose yarn made during machine start-up were analyzed to verify the consistency of numerical simulation results.The methods were as follows: based on the three conservation equations,the Realizable k-? modal equation and the wall function method were employed to solve the equations,the airflow area was divided by a tetrahedral mesh with good adaptability,and then the movement and development of the airflow field was simulated,and the spinning experiment was conducted to verify the simulation results,which lays a foundation for the study of airflow/fiber coupling interaction.In chapter 3,the motion trajectory and distribution characteristics of the airflow field after the high-speed airflow enters the nozzle and forms a high-speed swirling airflow were studied.Due to the effect of calculation and multi-boundary,mixed tetrahedrons and hexahedrons were used to redivided the grids,and dynamic meshing technology was used to conduct the simulation;and under the various boundary conditions and fiber existence conditions,the motion characteristics of the high-speed swirling airflow in the normal spinning process was simulated,the distribution characteristics of pressure field,velocity field,turbulence field,temperature field and airflow track of the airflow and so on were revealed in detail,and preliminary qualitative prediction the effect of airflow rotation on fiber twisting under multi-boundary conditions was obtained,which lays a foundation for chapter 4 to study the motion law of fiber in high-speed airflow field.(2)study on the mechanism of airflow/fiber coupling under the action of high-speed swirling airflowThe second order nonlinear double asymptotic method was used to study the law of airflow/fiber coupling under the high-speed swirling airflow in the stable spinning process,and the kinematics and dynamics conditions of airflow and fiber interaction after the gas-solid two-phase coupling was explored;the nonlinear large deformation problems such as tension,bending and torsion of free-end fiber under airflow were discussed,and the coupling mechanism of airflow/fiber under high-speed swirling airflow was clarified,which lays a theoretical foundation for the dynamic simulation of single free-end fiber twisting process under high-speed airflow.(3)study on the dynamic process of fiber separation and aggregation and the mechanism of wrapping and twisting under the action of high-speed swirling airflowThe three-dimensional numerical computational dynamics model of a single fiber with free-end was improved,fiber/airflow/wall system contact model was built,and the force equation of fiber/airflow/wall was established by combining contact mechanics and friction mechanics,the dynamic evolution process of fiber separation and aggregation under the action of high-speed rotating airflow was simulated;the dynamic evolution of the fiber with free-end being stretched,bent or twisted under the airflow force were studied;qualitative and quantitative experiments were carried out to observe the dynamic process of separation of single free-end fiber from the center of the yarn body;the number and degree of the free-end fiber wrapping to the yarn body were analyzed in combination with spinning experiments to study the effect of wrapping effect on the strength of vortex yarn.Therefore,the mechanism of wrapping and twisting of fiber with free-end was clarified,which lays the theoretical foundation for the control mechanism of using air to wrap and twist the yarn.This paper combines qualitative and quantitative methods to verify the rationality of gas-solid coupling research method.There were two qualitative methods: one was to use water flow instead of air flow and use single yarn to observe the movement of single yarn in water flow;the second,the morphology and changes of a single free-end fiber in spinning state under the action of high-speed rotating airflow were preliminarily observed with the aid of a high-magnification microscope.The quantitative method was used to verify the rationality and accuracy of the simulation results of fiber motion and airflow field,by seperately comparing and analyzing the two parameters of the horizontal displacement of the intermediate point when a single free-end fiber motion and the amount of airflow into the twisting chamber.The results show that the numerical simulation results are in good agreement with the experimental results,which shows that dynamic numerical simulation can better solve the difficult problem of dynamic fiber separation and condensation that is difficult to be observed in the experiment.It has certain theoretical guiding significance for the application of airflow technology in textile field. |
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