Flow past a sphere

The flow passing a sphere is perhaps the most simple setup to study the aerodynamics of blunt bodies. This simple setup is characterized by a single dimensionless parameter, being the Reynolds number ( $Re$ ), $Re = \frac{UD}{\nu}$ , with $U$ the overall speed, $D$ the diameter of the sphere and $\nu$ the kinematic viscosity. The visualization here concerns a setup where the Reynolds number gradually increases from $Re = 200$ to $Re = 2000$ . This gives rise to a turbulent wake, which is visualized using volumetric rendering. The wake is defined here as the region where the flow speed is less than 90% of $U$ . Fully stagnant flow ( $|\vec u| = 0$ ) is colored red, and transitions via white to blue for $|\vec u| = 0.9U$ , with increasing transparency.

An alternate visualization focuses of the vortex structures in the wave. The movie below shows an iso-surface of the $\lambda_2$ vortex-detection criterion of Jeong and Hussain (1995).