In air jet looms, the weft yarn is transported from the prewinder to the reed by means of an air flow. In this work, the motion of a yarn inside a main nozzle during the first stage of an insertion process is modeled and analyzed. In this stage, the weft yarn is clamped at one side and free at the other side. Therefore, the deformation waves of a clamped–free yarn are modeled. A three-dimensional, two-way, fluid–structure interaction simulation has been performed in which the yarn is represented as a flexible cylinder and the arbitrary Lagrangian–Eulerian technique is employed. The results of the simulation have been compared quantitatively and qualitatively with experiments. It was, however, not possible to match the initial position and stress state of the yarn in the simulations to that in the experiments. This causes large differences between the simulated and measured yarn positions and wave characteristics, especially at the beginning. The agreement between experimental and simulated wave characteristics notably improves as time progresses, but substantial differences remain. Analyzing the overall motion of the yarn inside the main nozzle shows that the mixing region, where the shocks are located, can be considered as an excitation point. In this point, the aerodynamic normal forces are high if the yarn is not located on the axis of the main nozzle. All deformation waves start from the mixing region and propagate along the yarn.
This research analyzes the interaction between fibers and the air jets that are used to accelerate them in fiber processing industries. Typically, supersonic flow is used to achieve sufficiently high thread speeds. However, this flow contains shocks and expansions, resulting in large longitudinal variations in force on the thin and flexible thread. Consequently, a complex fluid-structure interaction (FSI) occurs between the supersonic air flow and the thread. In this research, the fluid-structure interaction between a supersonic air flow and a thread is studied numerically using three-dimensional simulations. The thread is represented by a smooth and flexible cylindrical body. The displacement of the thread is calculated for a given traction on its surface using a finite element structural dynamics code. The compressible flow around the thread is calculated using a finite volume computational fluid dynamics (CFD) code, using the arbitrary Lagrangian-Eulerian (ALE) framework to account for the thread deformation. In these partitioned simulations, the kinematic and dynamic equilibrium conditions on the fluid-structure interface are satisfied using a coupling algorithm. Two coupling algorithms are compared and the influence of numerical parameters is investigated. The fluid-structure interaction simulations reveal transversal running waves in the thread. By comparing the speed of these waves with the propagation speed of the shock waves in the tube, it can be concluded that these phenomena are not related.
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