Three-dimensional wake dynamics and vortex-induced vibrations of circular and hexagonal cylinders

Abstract

In the present work we conducted a deep investigation on identifying geometry and orientation-dependent effects on three-dimensional wake dynamics and fluid–structure interaction. The study employs a coupled Lattice Boltzmann method and Immersed Boundary Method to investigate the flow past hexagonal cross-section cylinders under two different orientations with respect to the free stream: one with a flat face perpendicular to the freestream and one with a corner aligned in the direction of the flow. The analysis spans different flow regimes, with Reynolds numbers ranging from 20 to 103. The framework adopts a Large Eddy Simulation approach based on the Smagorinsky subgrid-scale model for the highest Reynolds numbers investigated (Re = 500 and Re = 1000). Validation of the numerical method involved comparing simulated drag and lift coefficients, as well as surface pressure distributions with benchmark data obtained from traditional Navier–Stokes solvers. The aerodynamic behavior of the hexagonal cross-section cylinder was then compared to the circular cylinder case to highlight the influence of cross-sectional geometry on wake dynamics, showing that the orientation of the hexagonal cylinder significantly alters the wake topology and promotes the early transition to a three-dimensional wake structure. The study further focuses on the Vortex Induced Vibration problem at Re = 200. In this context, the solid-to-fluid density ratio is kept constant among the different test cases at 10, while the ratio among the pulse of the lift fluid force and the natural frequency of the system is set at two different values 0.5 and 0.9 to investigate how the wake dynamics is affected by the displacement of the obstacle.