Multispecies Bhatnagar$-$Gross$-$Krook models and the Onsager reciprocal relations

TL;DR

This paper investigates the limitations of common Bhatnagar-Gross-Krook models in satisfying Onsager reciprocal relations, highlighting issues in their calibration for accurate transport property modeling.

Contribution

It demonstrates that most velocity-independent Bhatnagar-Gross-Krook models fail to satisfy Onsager relations, revealing a fundamental limitation in their physical consistency.

Findings

Most existing models do not satisfy Onsager relations

Velocity-independent coefficients cause calibration issues

Transport properties may not match real fluids

Abstract

It is shown that most of the existing versions of the Bhatnagar$-$Gross$-$Krook model $-$ those whose coefficient are independent of the molecular velocity $-$ do not satisfy the Onsager relations. This circumstance poses a problem when calibrating these models, making their transport properties match those of a specific fluid.