Vortex Induced Vibration of a cylinder, which is modeled using dynamic mesh methods, is a complicated and important process in the interaction between fluids and structures. This process happens when fluid flows past a cylinder-shaped body and the loss of vortices makes it twist and turn. This method records the complex interaction between the moving structure and the flow of fluid, giving important information about the patterns of vortex loss and the forces that affect the cylinder. The present study is conducted based on two invaluable reference papers:

• Reference [1]: Asyikin, Muhammad Tedy. CFD simulation of vortex induced vibration of a cylindrical structure. MS thesis. Institutt for bygg, anlegg og transport, 2012.
• Reference [2]: Izadpanah, Ehsan, Yasser Amini, and Ali Ashouri. “A comprehensive investigation of vortex induced vibration effects on the heat transfer from a circular cylinder.” International Journal of Thermal Sciences125 (2018): 405-418.

Figure 1: Schematic diagram of Vortex Induced By Cylinder Vibration [2]

Simulation Process

The two-dimensional geometry diagram can be easily designed using ANSYS Design Modeler. Although the grid undergoes multiple modifications during the cylinder vibration, an initial tetrahedron grid concentrating on the region behind the cylinder is required in the first place. To be more specific, the grid will be modified by Smoothing methods during the solution. These techniques are available when Dynamic Mesh is enabled. More importantly, the vibration is applied by a user-defined function (UDF) to the cylinder.

Figure 2:: Vortex Induced By Cylinder Vibration (Dynamic Mesh) CFD Simulation

Post-processing

The turbulence kinetic energy (TKE) shows an interesting vortex street pattern in the cylinder’s wake, with areas of high and low energy that change over time. This typical von Kármán vortex street has a sinusoidal wake structure, meaning that the TKE is strongest right behind the cylinder and slowly fades away downstream. This pattern makes it clear that the cylinder’s oscillating motion affects the vortex loss process. This creates a feedback loop between the fluid dynamics and the structure’s vibration. The velocity curve shows more of the complicated flow patterns that the cylinder’s vibrations cause. Around the cylinder, areas of high velocity (red) and low velocity (blue) can be seen alternating. These areas relate to areas where the flow speeds up or slows down. The unevenness in the speed field close to the cylinder is especially interesting because it shows the cylinder’s rapid direction of motion and how it affects the fluid around it. The mesh picture shows the dynamic mesh, which shows that the modeling can change based on how the cylinder moves. There is a finer mesh near the cylinder and in the wake region to show the fine-scale flow structures correctly. This adaptive meshing is very important for understanding how the boundary layer moves and how vortices form, which are needed to correctly guess the forces pressing on the cylinder and how its structure will react.

Figure 3: Wake region behind vibrating cylinder CFD Simulation

Figure 4: Mesh adaption by Dynamic mesh in vibrating cylinder CFD Simulation