Dynamics of a long flexible filament conveyed in the near field of a turbulent jet

Abstract

This study numerically investigates the conveyance of a long flexible filament in the near field of a jet flow using the immersed boundary-lattice Boltzmann method (IB-LBM) and large eddy simulations (LES). The filament is introduced into the jet flow field from an external domain, delivered by a turbulent jet at a Reynolds number of 4500. This research analyzes the filament's dynamics and morphological evolutions, highlighting the effects of bending stiffness (K_b*), linear density (m_f*), and initial velocity (U₀*) on conveyance stability. Initially, the filament exhibits stable forward motion with minimal fluctuations in the jet's potential core region. However, as the filament's leading section enters the developing region, a bulging shape forms in the middle section, leading to instability and morphological fluctuations. Increasing m_f* and U₀* enhance conveyance stability by delaying the bulging formation in the middle section and reducing morphological fluctuations. The leading section of the filament experiences the most significant fluctuations, suggesting that inertia effects dominate upstream. Varying K_b* primary affects the filament's behavior post-instability while does not significantly impact the position of instability onset. Additionally, when U₀* is less than half of the inlet airflow speed, the morphological fluctuations are significantly amplified. To improve conveyance stability for long filaments under similar conditions, it is recommended to accelerate the filament to at least half of the inlet jet velocity. These findings provide insights into optimizing long filament conveyance in industrial processes and biomedical applications, where precise control of filament behavior is crucial.