Numerical Investigation of Laminar Flow and Heat Transfer in a Bifurcated Backwards-Facing Step in the Presence of an Elastic Fin

Passive Flow Control in Pipelines is gaining increased importance in the field of fluid transport, particularly in oil and gas applications. This approach relies on the installation of passive devices designed to alter fluid flow paths by generating suppression zones. Among these devices, fins are particularly notable. Hence, the objective of this paper is to provide a numerical investigation into the behavior of laminar flow within a bifurcated backward-facing step (BFS), controlled through the installation of a flexible fin at the lower wall of the enlarged duct part, with varying mechanical stiffness and positioning. The study considers a flow through an expanded conduit, where the fluid enters with a predefined velocity profile and subsequently splits into two sub-conduits. The investigation focuses on examining the influence of fin length (0.5 ≤ L c / H ≤ 1), position (4 ≤ x 0 / H ≤ 7), and elasticity on the elasto-hydrodynamic structure of the flow, including vortex formation, flow separation, the maximum displacement of the flexible fin, and the efficiency of the sub-conduits at the outlet. This analysis is governed by the momentum equations, coupled with solid mechanics equations, using the Arbitrary Lagrangian-Eulerian (ALE) framework. The governing equations are solved using the finite element method, implemented through the simulation and the sliding mesh technique in COMSOL Multiphysics 5.7. The numerical results reveal that installing a flexible or rigid fin within the BFS system significantly impacts the non-isothermal flow behavior within the bifurcation ducts. This configuration effectively allows for flowrate regulation at the BFS outlet, also making it possible to equalize flow rates under specific conditions, particularly when using longer fin that extend halfway across the channel. Moreover, the fin placement on the bottom is important for achieving effective flow rate control and heat transfer, aligning with desired requirements for each branch outlet.