Turbulence

Introduction

Trubulence is a facinating field of research due to the complex patterns that can evolve in turbulent flows. Turbulence is omnipresent as it occurs whenever objects move fast in a fluid. For example, birds use wing tip vortices to save energy during long vojages by flying in V formation. Cars produce vortices causing noise and waste of fuel.
Yet another example is the sound that emerges from the moving hands of a Karate master, or the sound caused by wind blowing by a chimney. In these flows a Kármán vortex street is present.



Kármán vortex street

The flow around a blunt body can crate a Kármán vortex street for Reynolds numbers above 90. In that flow regime the flow detaches from the body creating a vortex on alternating sides. The repeating structure of the flow can be preceived as sound.

The video below shows a Kármán vortex street behind a cylinder. The denisty of the gas (nitrogen) is 2.325e-5 kg/m^3, the diameter of the cylinder is 1 m, the velocity far away from the cylinder is 300 m/s and the temperature is 298 K. The Reynoldsnumber is about 390.

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Download video: MP4 OGV



This simulation was performed on a workstation with four AMD Opteron 6272 and took about 4 days to complete.

Conclusions

PI-DSMC can be used to study turbulent flows for arbitrary bodies and flow conditions.