Von Kármán Effect over Cylinder, ANSYS CFX

This project simulates the Von Kármán vortex street behind a cylinder using ANSYS CFX software in both steady and transient (time-dependent) forms.

The Von Kármán vortex street is a repeating pattern of swirling vortices caused by fluid flow separating and shedding behind blunt objects like a cylinder. This creates unsteady flow patterns downstream.

The geometry is 2.5D with a 0.5m diameter cylinder centered in the flow domain. Air enters at 0.1 m/s. The mesh uses high-quality tetrahedral elements refined near the cylinder via the Body of Influence feature, with 10 inflation layers for boundary layer capture, totaling 77,262 elements.

Two simulations are run: steady and transient, including gravity effects and a surface tension coefficient of 0.072 N/m between air and water. The turbulence model is the Shear Stress Transport (k-ε SST). The solver uses high-resolution schemes for advection and turbulence, with a second-order backward Euler time discretization in transient runs.

Results show characteristic vortex shedding behind the cylinder forming a Von Kármán vortex street. Flow asymmetry causes pressure variations that lead to periodic lateral forces on the cylinder, potentially causing vibrations. Visualization includes 2D contours, vectors, and streamlines of velocity, pressure, and turbulence kinetic energy, with animations displaying the repeating vortex patterns.

This simulation captures the complex fluid dynamics of vortex shedding accurately and highlights the aerodynamic forces on bluff bodies.