Abstract
Vortex-induced vibrations (VIV) of hexagonal cylinders at Reynolds number of 1000 and mass ratio of 2 are studied numerically. In the numerical model, the Navier–Stokes equations are solved using finite volume method, and the fluid-structure interaction (FSI) is modelled using Arbitrary Lagrangian Eulerian (ALE) Scheme. The numerical model accounts for the cross-flow vibration of the cylinders, and is validated against published experimental and numerical results. In order to account for different angles of attack, the hexagonal cylinders are studied in the corner and face orientations. The results are compared with the published results of circular and square cylinders. Current results show that within the studied range of reduced velocities (up to 20), unlike circular and square cylinders, no lock-in response is observed in the hexagonal cylinders. The maximum normalized VIV amplitudes of the hexagonal cylinders are 0.45, and are significantly lower than those of circular and square cylinders. Vortex shedding regimes of the corner-oriented hexagons are mostly irregular. However, in the face-oriented hexagons, the shedding modes are more similar to the typical P + S and 2P modes.
Highlights
Vortex-induced vibration (VIV) is a major concern in design of slender structures exposed to the wind flow, such as: high-rise buildings [1,2] and bridges [3,4,5], or subject to water currents, such as: offshore platforms [6,7] marine risers [8,9,10] mooring elements [11,12,13], free spanning pipelines [14,15,16], or under action of other types of flow such as: heat exchanger tubes [17,18,19] and reactors [20,21]
In the case of vortex-induced vibration, vibrations can be in two dimensions because of time-dependent drag and lift forces, as the vortices are shed from the bluff body [24]
This study aims to investigate the cross-flow VIV response of hexagonal cylinders with m* = 2 at Re = 1000
Summary
Vortex-induced vibration (VIV) is a major concern in design of slender structures exposed to the wind flow, such as: high-rise buildings [1,2] and bridges [3,4,5], or subject to water currents, such as: offshore platforms [6,7] marine risers [8,9,10] mooring elements [11,12,13], free spanning pipelines [14,15,16], or under action of other types of flow such as: heat exchanger tubes [17,18,19] and reactors [20,21]. Two fundamental experimental studies on cross-flow VIV of circular cylinders with one degree of freedom (1-DOF) were conducted by Feng [25] and Khalak and Williamson [26] These pioneering studies showed that the VIV response is significantly related to the mass ratio, m* and the reduced velocity Vr. Mass ratio is defined as m* = m/md (the structural mass m divided by the displaced fluid mass md). Zhao et al [41] conducted numerical simulations of VIV of a square cylinder with m* = 3, Re = 100, and at angles α = 0◦, 22.5◦ and 45◦, using Petrov-Galerkin finite element method They reported 2S vortex shedding mode in all reduced velocities (1 < Vr < 30) for α = 0◦. The lift and cross-flow vibrations as well as vortex shedding regimes at reduced velocities between 2 and 18 of face-oriented and corner-oriented hexagonal cylinders are discussed
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