Vortex flow generated by a magnetic stirrer

American Journal of Physics, Vol. 75, 1092-1098 (2007). We investigate the flow generated by a magnetic stirrer in cylindrical containers by optical observations, PIV measurements and particle and dye tracking methods. The tangential flow is that of an ideal vortex outside of a core, but inside downwelling occur with a strong jet in the very middle. In the core region dye patterns remain visible over minutes indicating a pure stirring and mixing property in this region. The results of quantitative measurements can be described by simple formulas in the investigated region of the stirring bar's rotation frequency. The tangential flow turns out to be dynamically similar to that of big atmospheric vortices like dust devils and tornadoes.