Dual Cascades in Axisymmetric Turbulence
Résumé
A spectral analysis of strictly axisymmetric turbulence is performed. We investigate in particular by direct numerical simulation the possible cascades of energy and helicity. Decaying and forced flows at moderate Reynolds numbers are considered. A dual cascade, in which energy is transferred to the large scales and helicity to the small ones, is first evidenced in helical flows. A similar scenario is then shown to hold in the absence of a net helicity: in this case, energy also cascades to the largest scales, and positively and negatively polarized helicity are transferred to the small ones.