First-principles predictions for shear viscosity of air components at high temperature.

Area of Science:

• Thermodynamics and Fluid Mechanics
• Computational Physics
• Chemical Physics

Background:

• Shear viscosity data is essential for accurate fluid dynamics simulations, especially at extreme temperatures.
• Existing experimental data is limited at high temperatures, necessitating advanced simulation methods.
• Ab initio potential energy surfaces (PESs) offer a fundamental approach to molecular interactions.

Purpose of the Study:

• To determine shear viscosity for non-reacting air and its components using direct molecular simulation (DMS).
• To validate DMS predictions against experimental data and other computational methods.
• To assess the accuracy of DMS-derived viscosity data compared to values used in computational fluid dynamics (CFD) codes.

Main Methods:

• Simulating isothermal, plane Poiseuille subsonic flows using the direct molecular simulation (DMS) method.
• Estimating shear viscosity by fitting DMS velocity profiles to the Navier-Stokes equations' analytic solution.
• Utilizing ab initio potential energy surfaces (PESs) as the sole input for atomic-level interactions.

Main Results:

• DMS shear viscosity predictions show excellent agreement with experimental data for N2, O2, and air up to 2000 K.
• Results align well with previous quasi-classical trajectory (QCT) calculations for pure N2 and O2.
• Ab initio shear viscosity data are generally lower than those in popular CFD codes across a broad temperature range.
• Wilke's mixing rule accurately predicts DMS air viscosity from component data up to 4000 K.

Conclusions:

• Direct molecular simulation is a reliable method for obtaining high-temperature shear viscosity data for air and its components.
• The study provides valuable, accurate viscosity data that can improve CFD simulations.
• The findings highlight potential discrepancies between fundamental simulations and current CFD models, suggesting areas for refinement.