New Classes of Conservation Laws Based on Generalized Fluid Densities and Reynolds Transport Theorems

TL;DR

This paper introduces a new framework for the Reynolds transport theorem that generates multiple generalized conservation laws for fluid systems using probabilistic densities and symmetry transformations.

Contribution

It presents 11 new formulations of the Reynolds transport theorem based on a generalized framework, expanding the set of conservation laws in fluid dynamics.

Findings

11 new conservation law formulations derived

Application to eight key conserved quantities

Expansion of analytical tools for fluid flow systems

Abstract

The Reynolds transport theorem occupies a central place in fluid dynamics, providing a generalized integral conservation equation for the transport of any conserved quantity within a fluid, and connected to its corresponding differential equation. Recently, a new generalized framework was presented for this theorem, enabling parametric transformations between positions on a manifold or in a generalized coordinate space, exploiting the underlying multivariate Lie symmetries associated with a conserved quantity. We examine the implications of this framework for fluid flow systems, within an Eulerian position-velocity (phase space) description. The analysis invokes a hierarchy of five probability density functions, which by convolution are used to define five fluid densities and generalized densities appropriate for different spaces. We obtain 11 formulations of the generalized Reynolds transport theorem for different choices of the coordinate space, parameter space and density, only the first of which is known. These are used to generate 11 tables of integral and differential conservation laws applicable to these systems, for eight important conserved quantities (fluid mass, species mass, linear momentum, angular momentum, energy, charge, entropy and probability). These substantially expand the set of conservation laws for the analysis of fluid flow and dynamical systems.