| The vortex-induced vibration flow around cylinders exhibits a complex coupled motion behavior between fluid and solid that is of great interest for many mechanical, ocean and aerospace engineering problems, which also brings a great challenge to numerical simulation.In the present paper, a direct numerical simulation of the vortex-induced vibration using direct force/fictitious domain method has been performed for a cantilevered flexible cylinder in axial flow, analyzing how dimensionless parameters including Reynolds number, the shear modulus, the density ratio of solid to fluid effect on the oscillation as well as the structure of vorticity and regular of vortex shedding in the flow field.The numerical results indicate that the vibration of the cylinder shows a flapping dominated symmetric character when it conducts a planar vibration. The frequency of oscillation increases as the density ratio declines or the Reynolds number and shear modulus rises, in which the effect of the latter is very small, on the other hand, the amplitude becomes larger as the Reynolds number and the density ratio increases but becomes smaller due to the increasing of shear modulus, in addition, the impact of density ratio on amplitude is much larger than that of Reynolds number and shear modulus. The maximum of dimensionless amplitude can be up to 0.08. Vortex shedding is mainly characterized symmetric hairpin vortices.The results obtained also show that the free ending of the cylinder is gradually circling which means the oscillation amplification occurs when the restraint in one direction of the planar vibration is released. In the case of "circle" vibration mode, the cross amplitude approximately equals to that of the vertical direction and the composite oscillation exhibits the character of good symmetry and unimodality, however, in the case of "ellipse" vibration mode, the cross amplitude is smaller than that of the vertical direction and the composite oscillation exhibits the character of double peak without symmetry. The variation of amplitude is similar to what is mentioned about the planar vibration and is still sensitive to density ratio. The maximum of amplitude can be up to 0.12. The frequency declines as the density ratio increases and at the same time it is influenced by the shear modulus in two different modes. Reynolds and dimensionless shear modulus have a restraint effect on each other. Initial conditions set without much effect on the vibration modes. "Circle" mode trailing vortex shedding appeared very interesting phenomenon which shade continuous revolving hairpin vortex. |
