A plume of smoke
A small localized heat source is often associated with a warm rising laminar jet that transitions into an irregular flow. This is showcased in the Schlieren photo below.
A simulation of such a setup is rather simple. Only a localized buoyancy source should suffice to capture the essence of the phenomenon shown in the photo. In order to visualize the simulation results, I added a virtual “smoke” tracer. The result of a volumetric rendering is shown below.
Additionally, the move below shows the effect of an increased Reynolds number of the evolution of the plume (i.e. a larger plume, a warmer plume and/or decreased viscosity). You can clearly see the emergence of relatively smaller flow structures near the base of plume, resulting in more efficient mixing with the environment.