The marriage of gas and dust

TL;DR

This paper reformulates dust-gas mixture equations into a single fluid model with diffusion, simplifying simulations and clarifying the physics of strongly coupled dust and gas systems.

Contribution

The authors introduce a new single fluid formulation for dust-gas mixtures that addresses numerical challenges and enhances physical understanding.

Findings

Reformulated dust-gas equations as a single fluid with diffusion.

Resolved numerical issues in simulating strongly coupled dust and gas.

Clarified the physical interpretation of dust-gas interactions.

Abstract

Dust-gas mixtures are the simplest example of a two fluid mixture. We show that when simulating such mixtures with particles or with particles coupled to grids a problem arises due to the need to resolve a very small length scale when the coupling is strong. Since this is occurs in the limit when the fluids are well coupled, we show how the dust-gas equations can be reformulated to describe a single fluid mixture. The equations are similar to the usual fluid equations supplemented by a diffusion equation for the dust-to-gas ratio or alternatively the dust fraction. This solves a number of numerical problems as well as making the physics clear.