  The expansion of Bose-Einstein condensates (BECs) is numerically studied.
Usually, the aspect ratio of a condensate is inverted due to the anisotropy of
the uncertainty principle. In turbulent BECs, however, the aspect ratio remains
constant. The reason for this phenomenon is still unknown, being a challenging
topic in the study of quantum turbulence. Here, the two-dimensional
Gross-Pitaevskii equation is solved and the time development of the aspect
ratio and of the radii of the condensates are calculated in the presence of
vortices. The results indicate that vortex pairs must be added to a condensate
in order to expand it while maintaining its aspect ratio. The anisotropy due to
the vortex pairs competes with that due to the uncertainty principle so that
the aspect ratio remains constant.
