Numerical Simulation Of Airflow-fiber Interaction By Immersed Boundary Lattice Boltzmann Method

Airflow-flexible-structure interaction phenomenon is very common in pneumatic-type textile field.Apart from theoretical method and experimental way,numerical method is now the most popular way to study fluid-structure-interaction problems and is drawing more and more attentions form scholars all over the word.However,flexible bodies,for instance,fibers and yarns,usually have large aspect ratio and high flexibility,which made them easy to deform and move significantly during the pneumatic delivery process.This makes conventional FSI solvers which rely on the body-fitted grid method hard to efficiently handle flexible-structure-fluidinteraction problems.In this paper,a computationally efficient non-body-fitted numerical method for airflow-fiber coupling is developed,namely,the momentum exchange based immersed boundary-lattice Boltzmann method,to study flexible fiber's movement characteristics in confined channel in low-Reynolds-number flow condition.The numerical study is carried out in order to give theoretical basis to the improvement of yarn qualities as well as the optimization of rotor spinning unit.Besides,we hope our attempt of applying IB-LBM to the textile research field may bring some inspiration to other scholars.The mathematical model for fiber movement,the basic idea of IB-LBM,the main related formulas and the principle of unit conversion between physical unit and lattice unit are briefly introduced at first.Then,two simple validations are performed to verify the accuracy of the developed algorithm on rigid immersed boundary and flexible immersed boundary.After that,the fiber model and its corresponding equation of motion are given and numerical simulation of the delivery of a single fiber in a fiber transport channel(FTC)is carried out.Two parameters,the inclination degree of the FTC and the initial configuration of the fiber,on the fiber conveyance are particularly investigated,and some conclusions on fiber conveyance in low-Reynolds-number flows have drawn as follows.1).Providing with the desirable accuracy,IB-LBM can efficiently deal with the interaction of fluid and rigid boundary or flexible body that involves large deformation.Thus,it can be applied to the pneumatic-type textile field.2).The inclination-type FTC is more efficient in fiber conveyance,and the larger the inclination angle tan? is,the sooner the fiber can be delivered to the outlet of FTC.3).For the fiber that has a completely straightened initial configuration,no matter how the inclination angle varies,the fiber always keeps a straight state during its delivery.4).For the fiber that has a wavy initial configuration,its delivery in FTC with different inclination angles differs.A larger inclination angles helps to straighten the fiber.Therefore,design the FTC in a more narrowing shape can improve the delivery of wavy fibers.5).Except the fiber that has a completely straightened initial configuration,other 4 configurations will experience varying deformations.The inclination-type FTC will improve the conveyance of the following 3 type of fibers,which is bulged in the middle,hooked in the tail and wavy configuration,by enhancing their straightness before they enter the rotor channel.However,for the initial fiber state with hook in the head,the hook will gradually become a fold,which may deteriorate the subsequent yarn quality.Therefore,the two parameters,the pins of the opening roller and the connection angle between the opening roller chamber and the FTC,should be carefully chosen to avoid obtaining fiber with such kind of configuration at the channel inlet.