Quad-cascade picture of turbulence

Abstract

Although its ubiquitous emergence in nature and variety of systems, turbulence possesses spatio-temporal chaotic, intermittent fluctuations, and makes it impossible to be precisely predicted. Persistent attempts for almost a century have been devoted to capture the invariant laws and hidden deeply universality out of the vast disorder and chaotic nature of turbulence. The celebrated Kolmogorov -5/3 law is robust, but not comprehensive to describe the diverse turbulences, especially in the turbulence driven by external volume forces, e.g. thermal convection, electrokinetic turbulence and etc. Here, we reveal that the fluxes of kinetic energy and scalar variance must be highly coupled to establish a universal conservation law and consequently we successfully unify a much diversity of scaling laws. As an example, in a microfluidic electrokinetic turbulence, additional scaling of -5/3, -9/5 and -7/3 are experimentally found in the power spectra of concentration. With this proposed model, a full quad-cascade picture is eventually complete to unify the various scaling laws for the most complicated physical problem of turbulence.