Adiabatic fluid energy and thermodynamic closure
For a smooth inviscid, nonconducting fixed-composition fluid, D_ts=0 and ρD_te=−P∇·v, where e and s are internal energy and entropy per mass.
Key knowledge
For a smooth inviscid, nonconducting fixed-composition fluid, D_ts=0 and ρD_te=−P∇·v, where e and s are internal energy and entropy per mass. With E=e+|v|²/2, total energy obeys ∂_t(ρE)+∇·[(ρE+P)v]=ρg·v. An equation of state P=P(ρ,s) closes the smooth mass, momentum and energy equations.
Values and equations
D_ts=0; ρD_te=−P∇·v; ∂_t(ρE)+∇·[(ρE+P)v]=ρg·v; P=P(ρ,s)
- D_t
- Material derivative ∂_t+v·∇
- s
- Entropy per mass J kg⁻¹ K⁻¹
- e,E
- Internal/total kinetic-plus-internal energy per mass J kg⁻¹
- ρ
- Density kg m⁻³
- P
- Pressure Pa
- v
- Velocity m s⁻¹
- g
- Body acceleration m s⁻²
- t
- Time s
Conditions and scope
- Local thermodynamic equilibrium, fixed composition, no viscous heating, heat conduction or volumetric energy source; g is body acceleration.
- Derivation applies to smooth reversible material evolution. Irreversible shocks conserve total energy but can increase entropy. Constant s along each parcel does not require the same s in every parcel; heat conduction or dissipation adds entropy production terms.
Sources · 2
References
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Evidence and review
Thermodynamics and Statistical Mechanics (2016): Internal energy: Equations 6.82–6.89, dU=T dS−P dV at fixed particle number; rewrite per conserved parcel mass with specific volume 1/ρ. Classical Mechanics III 8.09 (2014): Chapter 6, fluid mechanics: §6.2 mass 6.25–6.28 and Euler momentum 6.32–6.34; total energy obtained by adding thermodynamic parcel work to velocity-dot-momentum, with explicit no-heat assumptions.
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