2.5D turbulence in non-Newtonian jets

We study the transition from 3D to 2D turbulence in planar jets of a power-law fluid at low Reynolds number. We use direct numerical simulations, in which we change the width of the computational domain, thus constraining the turbulent scale. We observe that the jet transitions from 3D to 2D turbulence as we reduce the width of the domain in the spanwise direction. We find a configuration with the simultaneous coexistence of 2D and 3D (or 2.5D) turbulence for intermediate domains. The analysis of the power spectrum shows the traditional Kolmogorov’s scaling for 3D turbulence, and we identify the inverse cascade in 2D turbulence, where energy is fed back onto the large scales. Cases with 2.5D turbulence show the 3D turbulence scaling close to the inlet, where the jet is thin, while flow structures far from the inlet follow a 2D-like behavior, due to their larger size. The bulk statistics follow almost the same power-law scaling obtained for turbulent Newtonian planar jets, but cases with a strong 2D turbulence activity show a sudden increase of the jet thickness far from the inlet, due to the large size 2D vortices.