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Theory and simulation of shock waves: Entropy production and energy conversion
Bjørn Hafskjold1, Dick Bedeaux1, Signe Kjelstrup1
1PoreLab, Department of Chemistry, Norwegian University of Science and Technology (NTNU), Trondheim, Norway.
Physical Review. E
|August 20, 2021
Summary
We developed the Gibbs excess method (GEM) to calculate entropy production in shock waves. This new method aligns with other thermodynamic approaches and accurately models shock wave behavior using nonequilibrium molecular dynamics simulations.
Area of Science:
- Thermodynamics
- Fluid Dynamics
- Computational Physics
Background:
- Shock waves are complex phenomena involving rapid changes in thermodynamic properties.
- Understanding entropy production is crucial for analyzing irreversible processes in shock waves.
Purpose of the Study:
- To introduce and validate the Gibbs excess method (GEM) for calculating entropy production in shock waves.
- To compare GEM with existing entropy balance methods using nonequilibrium molecular dynamics (NEMD) simulations.
Main Methods:
- Developed the Gibbs excess method (GEM) based on nonequilibrium thermodynamics for surfaces.
- Employed nonequilibrium molecular dynamics (NEMD) simulations of a thermal blast in a one-component gas.
- Studied weak (M≈2) and strong (M≈6) shock waves with a Prandtl number of approximately 1.4.
Main Results:
- GEM provided consistent results with three alternative entropy balance methods.
- Internal energy showed minimal deviation from equilibrium in the shock front.
- Entropy production scaled with the square of the Mach number and occurred primarily within the shock wave (97%).
- Kinetic energy conversion in shocks was predominantly reversible into enthalpy and entropy.
Conclusions:
- The Gibbs excess method (GEM) is a reliable approach for analyzing shock wave entropy production.
- NEMD simulations confirm that shock waves behave consistently with Navier-Stokes equations and Rankine-Hugoniot conditions.
- Shock waves efficiently convert kinetic energy, with most entropy production localized within the wave itself.
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