喷气涡流纺喷嘴内气流流动的二维数值模拟

 为探讨喷嘴内部气流流动特征对纤维加捻成纱的作用,建立计算流体动力学(CFD)模型,对喷气涡流纺喷嘴中的气流流动进行二维数值模拟,并根据计算结果分析喷嘴内高速气流的速度场和压力场分布。模拟结果表明:气流的最大速度可达超音速,由于切向速度所产生的离心力和加捻作用,纤维的尾端从纤维束中分离出来,并旋转加捻到纤维束上,形成具有真捻的纱线;喷嘴入口区域的压力小于外界气压,这有利于由前罗拉钳口处输出的纤维束吸入喷嘴。研究还表明CFD技术是研究喷气涡流纺喷嘴内气流流动的重要手段。     

喷气涡流纺喷嘴参数对内流场特性的影响

为探究高速气流在喷气涡流纺内流道的流场特性规律,课题组基于FLUENT建立喷嘴的参数化模型,采用单一变量法分别研究喷孔数量、喷孔倾角和供气压力对喷嘴内流场的影响。结果表明：受引导部件的影响,内流场气流特性分别存在不规则性,且有较多的回流和涡流现象的存在;随着喷孔数量的增加,喷孔出口气流速度略有增大,内流场涡流现象减少,气流旋转性能显著增强;随着喷孔倾角的增大,气流速度峰值先增大后减小,导引部件螺旋面两侧的轴向速度和切向速度分布有明显不同,而当喷孔倾角超过70°后角度对速度的影响逐渐减弱;随供气压力的增加,气流速度增大,气流旋转特性增强,纱线加捻效果有所提高。该研究对于喷气涡流纺喷嘴的结构设计具有参考价值。     

基于有限元模型的喷气涡流纺纤维运动轨迹模拟

为模拟喷气涡流纺气流加捻过程中自由端纤维的运动轨迹,针对喷气涡流纺气流加捻过程中自由端纤维柔性体的动力学特点,基于弹性细杆单元建立纤维有限元模型,结合喷气涡流纺气流加捻腔内流场的气压、速度分布特征,确立自由端纤维柔性体有限元动力学微分方程,遵循力学平衡、能量守恒、质量守恒和动量守恒等原理,解析自由端纤维柔性体有限元动力学微分方程的待定系数,数值模拟自由端纤维在加捻腔内高速旋转气流作用下的运动轨迹;利用示踪纤维法对有限元模拟纤维运动轨迹的理论结果进行验证。结果表明,基于弹性细杆单元的有限元模型对于模拟纤维运动轨迹具有一定可行性和有效性。     

喷嘴参数对喷气涡流纺内流场特性的影响研究

为明确喷气涡流纺纱的纺纱机理,研究喷嘴中喷孔数量、喷孔倾角和供气压力对喷气涡流纺内流场的影响情况,文章采用Fluent软件进行喷气涡流纺的内流场模拟分析.通过结果对比分析发现:喷孔数量和供气压力对喷嘴内流场的气流旋转运动影响较为显著,随着喷孔数量和供气压力的增加,喷嘴内气流的旋转运动显著增强,对纱线自由端纤维的加捻效果...     

解析法评价旋转气流对喷气涡流纱的加捻强度

在对喷嘴内部流场数值模拟的基础上通过解析法研究旋转气流对喷气涡流纱加捻的强度。研究结果表明:旋转气流对喷气涡流纱的加捻强度是喷孔数目、喷孔倾角、喷孔直径、喷嘴直径、空心锭外径、喷孔出口速度(即喷嘴气压)、空心锭入口与喷嘴入口间距、尾端自由端纤维倒伏空心锭上部的高度、纱线直径等的函数。喷孔出口速度增加,旋转气流加捻强度增强;加捻喷嘴直径减小,旋转气流加捻强度增大;空心锭入口与喷嘴入口间距增加,旋转气流加捻强度减小;空心锭外径增加,旋转气流加捻强度增加。数值计算结果表明解析模型的有效性。     

喷气涡流纺喷嘴喷孔参数的分析

喷气涡流纺是利用喷嘴内高速气流的旋转对纤维加捻成纱的设备,为了分析喷嘴的结构参数对成纱质量的影响,选择喷嘴的喷孔直径d为0.5 mm,分别在不同喷孔数量n(5,6)及不同喷孔角度θ(60°,65°,70°,75°,80°)下,在新型涡流纺纱机上对粘胶原料进行纺纱实验。实验结果得到了喷孔最优结构参数:喷孔孔径×数量φ0.5×5;喷孔角度70°。     

应用STAR-CCM+的旋流喷嘴内部三维流场数值模拟与分析

在环锭细纱机上安装旋流喷嘴,能较好地减少细纱毛羽。应用软件STAR-CCM+对旋流喷嘴内部流场进行数值模拟,表征了喷嘴纱道流场的分布情况,解析喷嘴纱道中径向、切向、轴向三向速度分布规律。当喷嘴气道与纱道相交方向和相切点不同时,结合气流对纤维的作用,分析旋流喷嘴纱道中的气流分布规律。从模拟结果得出：旋流喷嘴纱道与气道相切点沿X轴负方向长度为14mm,且喷嘴气道与纱道相交方向向上时,所形成的气流可以减少占大多数的顺向毛羽。     

喷气涡流纺工艺参数对气流场影响的数值计算

通过数值计算的方法研究喷嘴结构参数及喷孔出口速度对喷嘴内部流场流动特征的影响。研究结果表明:喷孔倾角增加,喷嘴轴线负压先增大后减小,倾角为30°时负压最大;切向速度随喷孔倾角的增加而减小,轴向速度随喷孔倾角的增加而增大;喷孔出口速度越大,切向、轴向、径向速度越大,在喷嘴轴线上负压也越大;空心锭外径对喷嘴内气流速度值影响较小,但空心锭外径较小时可使喷嘴轴线上负压增大;随空心锭与喷嘴入口间距的增加,速度场呈减小趋势,喷嘴内部静压减小,喷嘴进口负压增大。     

喷气涡流纺纱线细节产生机制分析

通过数值计算对喷气涡流纺喷嘴内部流场衰减规律进行探讨。讨论加捻腔中纤维的受力情况及涡流作用下的运动状况;建立倒伏在空心锭上的纤维自由端绕空心锭旋转的临界角速度与进入纱尾的纤维头端长度、纤维半径等参数间的函数关系,以临界角速度作为衡量纤维头端是否被抽拔的依据,解释喷气涡流纺落纤、成纱细节产生的原因。临界角速度随进入纱尾纤维头端长度的增加而增大;纤维半径越大,临界角速度越小,在同一喷嘴气压下,半径大的纤维纺纱时落纤、成纱细节较多;增加喷嘴气压对成纱强力有利,超过某临界值落纤、成纱细节增加,对成纱质量不利;增加喷嘴内部负压,适当减小前罗拉与空心锭的距离可减少落纤、细节的产生。     

传统型与自捻型喷气涡流纺的对比

针对喷气涡流纺纱技术气流加捻过程中落纤率较高导致纱线细节较多以及纱线结构中芯纤维平行伸直导致纱线强力较低的问题,提出自捻型喷气涡流纺纱技术,依据动摩擦原理,采用镭射激光加工处理,增大自由端纤维与空心锭接触面之间的动摩擦力,实现纤维在空心锭表面旋转运动过程中自身发生扭转后包缠到纱线中,增大纤维间的抱合力。同时基于流体力学模拟和样纱试纺实验,对比分析了传统型喷气涡流纺和自捻型喷气涡流纺空心锭结构参数、喷嘴内部近壁面处的流场特征和纱线结构性能,验证了自捻型喷气涡流纺纱技术的可行性。     

Numerical simulation of the yarn formation process in Rieter air jet spinning

This paper presents a three-dimensional numerical simulation of the airflow field inside Rieter air jet spinning nozzle. The velocity and pressure distribution were analyzed to describe the principle of yarn formation. The analysis of velocity components and static pressure revealed how the air vortices are created inside the nozzle. A theoretical study along with experimental verification was performed to investigate the influence of nozzle pressure on air jet yarn tenacity and the results were in good agreement. The results show that increasing nozzle pressure resulted initially in improving yarn tenacity but at high pressure tenacity deteriorates.     

A numerical and experimental study on the effect of the orifice angle of vortex tube in vortex spinning machine

In order to study the effect of orifice angle of vortex tube on yarn forming in jet vortex spinning, eight levels of nozzle angle are designed, from 40° to 65°, and the corresponding three-dimensional computational fluid dynamics (CFD) models are established to conduct the numerical simulation of the airflow in the nozzle. Through the analysis of numerical simulation, the pressure and velocity distribution are made clear which provides reference for the future design of the vortex tube. Simulation results show that when the orifice angle is around 50°, the airflow state within the nozzle has a large negative pressure with appropriate axial and tangential velocity, which is conducive to the formation of the open ends of fibers and twisting, and the yarn quality is better. Spinning experiment results prove that single yarn strength is the maximum, the irregularity of single yarn strength is the minimum, and other yarn properties are superior with the orifice angle at 50°, which shows a good agreement with the simulation results.     

基于螺旋导引槽空心锭子的喷气涡流纺加捻腔流场模拟

针对喷气涡流纺纺纱过程中存在的成纱强力偏低的问题,提出一种基于螺旋导引槽空心锭子以提高成纱强力的方法。通过数值模拟的方法,研究基于螺旋导引槽空心锭子的加捻腔气流场流动特征,验证螺旋导引槽空心锭子结构对成纱性能的改善作用。结果表明：空心锭子外表面的螺旋导引槽可以引导气流流动,使自由尾端纤维的加捻作用增强;此外,螺旋导引槽结构的存在,导致槽内外气流的静压和速度存在差异,引起自由尾端纤维的内外转移,并产生自捻效应,可进一步实现喷气涡流纺纱线强力的提高。     

Research on flow field in a modified ring spinning system with the air nozzle

Twisting is one of the most important steps in the yarn spinning, which influences the geometry of spinning triangle and determines the properties of spun yarns. Airflow is one of the most important measures on improving yarn spinning. In this paper, a kind of air nozzle with vortex guiding channel was designed and used on the modification of ring spinning system, and the spun yarn qualities was studied by analyzing the airflow field in the nozzle. Firstly, the three-dimensional physical model of nozzle was given using CAD software according to the geometrical size of the practical nozzle model. Then, the numerical simulations of the three-dimensional flow field in the nozzle were given using Fluent software. Finally, two different kinds of yarns 10Ne and 20Ne were spun in the modified ring spinning system with the nozzle installed. The airflow pressure 0.01 Mpa and two different swirling directions, anticlockwise and clockwise, were chosen. The qualities of spun yarns, hairiness, strength, evenness, and number of snarling were measured and analyzed. It is shown that the high vortex airflow can be produced in the nozzle, and then corresponding twist can be produced. For the Z(S) twisting spun yarn, under the effects of the clockwise (anticlockwise) vortex airflow, the pre-twisting would be produced and the yarn twist can be strengthened, while under the effects of the anticlockwise (clockwise) vortex airflow, the untwisting effect would be produced, and the yarn twist can be decreased.     

喷气涡流纺纺纱过程中的气流场数值模拟

为明确高速气流成纱过程中气流产生和发展变化的规律,解决当前研究中存在的不足,对喷气涡流纺初始引纱过程和正常稳定纺纱过程的气流进行三维数值模拟及理论分析,并采用纺纱实验和借助扫描电子显微镜技术验证数值模拟结果。结果表明:纺纱初始时气流扰动小,湍流少,气流流线规则有序发展,喷嘴内负压气流产生强大吸力利于顺利引纱,模拟推测纤维的集束性较好,包缠和抱合效果较差;正常纺纱过程中气流场不稳定,湍流现象明显,气流轨迹复杂,并出现涡流和回流现象,回流为纱提供额外张力,利于提高纱线强力,模拟推测纤维的包缠和抱合效果较好,这也与纺纱实验结果相吻合。