Non-equilibrium length in granular fluids: From experiment to fluctuating hydrodynamics

Abstract

Velocity correlations in a 2D granular fluid are studied in experiments and\nnumerical simulations. The transverse component of the velocity structure\nfactor reveals two well defined energy scales, associated with the external\n"bath temperature" $T_b$ and with the internal granular one, $T_g<T_b$,\nrelevant at large and small wavelengths respectively. Experimental and\nnumerical data are discussed within a fluctuating hydrodynamics model, which\nallows one to define and measure a non-equilibrium coherence length $\\xi$,\ngrowing with density, that characterizes order in the velocity field.\n