Statistical fluid mechanics: Dynamics equations and linear response theory

Abstract

The statistical nature of discrete fluid molecules with random thermal motion so far has not been considered in mainstream fluid mechanics based on Navier–Stokes equations, wherein fluids have been treated as a continuum breaking into many macroscopically infinitely small (but microscopically large enough) mass elements with their motion only characterized by center-of-mass velocity. Here, we provide a Statistical Mechanical approach to address fluid dynamics by considering statistical velocity distribution of discrete molecules within macroscopically infinitely small volume elements as well as their center-of-mass velocity. Dynamics equations governing the evolution of physical variables have been proposed, Green's functions have been obtained, and the linear response theory has been applied to study physical situations with external heat perturbation. It is found that the propagation of heat, center-of-mass motion, and sound are intrinsically integrated in Statistical fluid dynamics. This work lays down the foundation for applications of Statistical fluid mechanics.