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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