Axial dynamics of viscous vortices.

Direct numerical simulations of viscous columnar vortices subject to a non uniform strain have shown that more or less uniform vortices can form even when the strain has zero spatial average, thus having compressing regions. According to the arguments of Jiménez & Wray (1994) this is due to the effect of axial waves that homogenize the core of the vortices regardless the fact that they are initially straight or not. In the present study it has been shown that the same mechanism works for unsteady strains, provided axial waves have enough time to develop along the vortex core. [ABSTRACT FROM AUTHOR]