Tensor-geometry-activated spectral energy transfer at Reynolds numbers of order unity in two-dimensional flows

We demonstrate that enhanced inter-scale energy transfer – a defining hallmark of turbulence – can be actively induced in Navier–Stokes flows even at Reynolds numbers of order unity. By reinterpreting the spectral energy flux as mechanical work resulting from the alignment between turbulent stress and large-scale rate of strain tensors, we show that, by actively enforcing geometric alignment between these tensors and amplifying the perturbation-induced stress, the flow exhibits scale-to-scale energy flux magnitudes comparable to those reported in the weakly turbulent regime of two-dimensional flows, even in the absence of dominant inertia. This study indicates that the mechanisms underpinning spectral energy flux are not exclusive to high-Reynolds-number turbulence but can extend into regimes previously deemed dynamically trivial. Our result also reveals a generic mechanism for directly accessing the same stress–strain-rate energy-flux pathway that underlies classical turbulence, but without the need for inertial dominance.