The von Kármán vortex street is an interesting fluid dynamics effect that happens when a fluid moves past a bluff body, like a round cylinder or a square object. The fluid separates from the flow when it hits the rough surface, creating vortices that are released in a regular pattern further downstream of the body. The von Kármán vortex street is a pattern of spinning vortices that happens over and over again. It is periodic and can be thought of as a series of organized, rotating flows that leave a wake behind the bluff body. In the current study which is conducted as an Advanced fluid mechanics course project, the splitter is welded to a cylinder (see Fig.1).

Figure 1: Schematic configuration of Von Karman vortex Street over bluff body

Simulation Process

Initially, the simple geometry model is produced by Desing Modeler. The bluff body is considered an extensive domain with a huge region behind it. Employing proper blocking helps us to generate a structured grid established from 43103 cells (see Fig.2). Given the Reynolds number, the flow regime remains laminar. Still, the formation of Von Karman vortex street is expected based on the fluid mechanics literature. The point is the phenomenon is time-based so a Transient (unsteady) solver is needed.

Figure 2: Structured grid – Von Karman Street Over Bluff Body CFD Simulation

Post-processing

With a lift coefficient (Cl) of 0.30475265 and a drag coefficient (Cd) of 1.073303, the CFD modeling of the von Kármán vortex street over a bluff body reports aerodynamic forces. A characteristic of the von Kármán vortex street phenomenon is that the bluff body experiences irregular lift forces due to the shedding of vortices behind. The relatively high drag coefficient shows that the body faces a lot of resistance as the fluid moves by. This is mostly because of the pressure drag that happens when flow separates and swirls form.

The animation and the contours show the flow field in motion, illustrating how the vortices shed off and are replaced by wake patterns. The velocity and pressure lines show the areas of changing high and low pressure that form downstream, which proves that the von Kármán vortex street exists. This contour makes it easier to understand the aerodynamic forces and gives us useful information about how the vortices changed over time and where they were located. Such a thorough study is needed to make sure that buildings that are subject to similar flow conditions, like bridges, towers, and chimneys, are stable and that the design is optimized. Vibrations caused by vortices could be very problematic in these places.

Figure 3: Velocity distribution around a bluff body CFD Simulation

Figure 4: Shed vortices behind a bluff body shown by streamlines