Counter-rotating vortices behind a heated cylinder

3D-transition behind a heated cylinder is studied at low Reynolds numbers. Both experimental and numerical techniques are used, including an electro-chemical tin-precipitation visualization method, a 2D High resolution Particle Velocimetry technique and a 3D Spectral Element Method. It is observed that the occurring spanwise velocity of the wake flow increases with the increase of the heat input to the cylinder. For Re=85 and Ri=1.0, distinct counter-rotating vortices are observed. Depending on the spanwise position, stagnation-like flows and jet-like flows are formed in the near-wake. Likewise, a difference in the flow topology is observed for 'in-plume' and 'out-of-plume' positions. Furthermore, a non-uniform temperature distribution is present in spanwise direction. This is associated with the accumulation of heat at certain spanwise positions, where the flow moves from the lower to the upper half of the wake. The upward flow motion at these spanwise positions seems to be induced by buoyancy when the temperature difference is large enough.