Generalized 3D Kolmogorov flow: effect of moderate large-scale damping

Turbulent flows can be understood as the superposition of a mean flow, which evolves slowly and is shaped by boundaries or forcing mechanisms, and a multitude of chaotic, short-lived fluctuations. We performed pseudo-spectral simulations of a turbulent three-dimensional Kolmogorov flow with large-scale damping on an aspect-ratio-three domain, which is driven by a sinusoidal shearing body force. The visualization shows the vorticity averaged over the direction normal to the forcing plane to emphasize the large-scale counter-rotating vortices. The bottom plot shows an effective wavenumber of the large-scale state. For this value of the damping parameter, the large-scale state switches frequently between two or three pairs of counter-rotating vortices, i.e. the k_s = 2/3 and k_s = 1 states. Please see for further details.