Vortex Flows Paint Themselves

G. E. Koppenwallner and D. Etling
Universit t of Hannover, Germany

The artistlike pictures of vortex flows presented here have been produced by the flow itself. The method of this natural flow visualization can be described briefly as follows: The working fluid is water mixed with some paste in order to increase the viscosity. Vortex flows are produced by pulling a stick or similar devices through the fluid or by injecting fluid through a nozzle into the working tank.

Figure 1

Figure 2

The flow visualization is performed in the following way: the surface of the fluid at rest is sparkled with oil paint of different colors diluted with some evaporating chemical. After the vortex structures have formed due to wakes or jets, a sheet of white paper is placed on the surface of the working fluid, where the oil color is attached to the paper immediately. The final results are artistlike paintings of vortex flows which exhibit a rich variety of flow structures.

Mixing in Regular and Chaotic Flows

C.-W. Leong and J. M. Ottino
University of Massachusetts at Amherst

These photographs show the time evolution of two passive tracers in a low Reynolds number two-dimensional time-periodic flow. The initial condition corresponds to two blobs of dye, green and orange, located below the free surface of a cavity filled with glycerine. The flow is induced by moving the top and bottom walls of the cavity while the other two walls...