Three-dimensional transition of a water flow around a heated cylinder at Re=85 and Ri =1.0

The three-dimensional flow transition behind a heated cylinder subjected to a horizontal flow (water is used as the working fluid; Pr=7) at a Reynolds number Re=85 and a Richardson number Ri=1.0, manifests itself in the far-wake as escaping mushroom-type structures from the upper vortices. The origin of the escaping mushroom-type structures lies in the generation of streamwise vorticity in the near-wake, which is described as a cyclic-process. In the presence of a spanwise temperature gradient in the near-wake, streamwise vorticity is generated, which results from baroclinic vorticity production. Due to these streamwise vorticity regions, low-speed flow will move upwards at so-called in-plume positions resulting in high- and low-speed streaks in the upper half of the wake. Next, `transverse' vorticity is generated by the spanwise gradients in the streamwise velocity component, resulting in counter-rotating vortices directly behind the cylinder. These vortices lead to high- and low-temperature regions in spanwise direction and the process repeats itself.