| Air-jet vortex spinning twist the fiber into yarn by spraying high speed airflow from the hole on the nozzle and then acting on the fiber.There is a complex fiber motion in the nozzle,which involves fiber-airflow two-phase coupling.The purpose of this thesis is to analyze the motion characteristics of the rotating airflow in the nozzle,and to study the fiber'motion law under the action of rotating airflow.The main contents of this thesis are as follows: By using the numerical simulation and experimental method to study the influence of the structure parameters of hollow-spindle on the distribution characteristics of flow field;on the basis of the structure of nozzle and hollow spindle in Murata No.861,the computational fluid dynamics model of air-jet vortex spinning is built;the motion law of flow field inside the nozzle is studied by using the FLUENT;and arranged inclined holes with annular array at the center of section of the hollow-spindle,analysed the influence of the number and angle of the inclined holes on the flow field;a two-dimensional nozzle model is established in ADINA,and the motion law of fiber is studied under different nozzle inlet pressure parameters and different inclined hole parameters.The nozzle structure is processed by transparent plexiglass and the nozzle experiment is set up.The effect of the posion of the hollow-spindle and the number of nozzle holes on fiber'motion in the airflow field is studied.The conclusions are drawn as follows:1.The compressed air will enter into the twisting cavity by a angular cut way at the outlet of the nozzle hole,then the airflow will appear spiral rotary motion and flow slowly towards the hollow-spindle'outlet,which is accompanied by the weakening of the flow velocity in the process.When the airflow reaches steady state in the nozzle,all the characteristic curves are symmetrically distributed in the central axis of the model.The static perssure distribution curve has a negative value at the entrance of the hollow-spindle,which will absorb the fiber into the inner channel and form the core fiber.2.The inclined holes on the hollow-spindle does not affect the distribution law of the velocity.That is to say,the inclined holes does not affect the twisting of the fiber,and has the following functions:By analyzing the axial velocity curve distribution on the center axis,wehave found that: the inclined holes can significantly increase the axial velocity of fiber and slow down the trend of axial velocity weakening,which is beneficial to the fiber to maintain a higher speed,increase its torsion effect,and then increase the fiber cohesion.3.The inclined holes on the hollow-spindle will affect the axial velocity of the fiber entrance of the nozzle'twisting cavity.Under the nozzle perssure inlet parameters remain unchanged,the axial velocity at the center of the fiber'entrance plane is increasd from20°'7.8m/s to 40°'8.9m/s and then decreased to 50°'8.3m/s,when the angle of the inclined hole is increased.4.The model established in ADINA is calculated under the condition of pressure inlet.When the air flow gradually jet from the orifice into the nozzle,the internal pressure distribution will be asymmetric,at the same time the fiber begins to swing,and then the fiber moves to the outlet in a wavy manner.With the increase of the inlet pressure of the nozzle,the swing amplitude of the fiber increases slightly,the swing frequency becomes faster and the swing period shortens.5.Inclined holes are installed on the hollow-spindle structure in the ADINA model.In the process of flow field,it is found that the presence of inclined holes causes the airflow inside or outside the nozzle,so that there are two times of fluid acting on the fiber,thereby affecting the movement state of the fiber.By analysing the fiber motion and velocity curves,we have obtained that the angle of inclined hole has a certain effect on the fiber movement and the fiber moves faster with the increase of angle;The fiber motion is the most intense when the angle of inclined hole is 40°.6.The motion modality of the fiber in the twisting cavity is proved through the nozzle experiment.We have found that: Under the action of tangential high speed airflow,the fiber which enter into the twisting cavity will revolve around the central axis of the nozzle.When fiber approaching the hollow-spindle,it will be attached to the conical surface outside the hollow-spindle and revolve around its central axis at the same time.Fiber has the most obvious rotation motion when the number of nozzle holes is 4 and the posion of the hollow-spindle is10 mm.The influence of the hollow-spindle on the airflow field and the fiber motion can provide a theoretical reference for further research on the spinning rule of air-jet vortex spinning. |
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