Compressible inviscid Euler momentum balance
For a smooth classical fluid with mass continuity, material acceleration is D_tv=∂_tv+(v·∇)v and inviscid momentum obeys ρD_tv=−∇P+ρg.
Key knowledge
For a smooth classical fluid with mass continuity, material acceleration is D_tv=∂_tv+(v·∇)v and inviscid momentum obeys ρD_tv=−∇P+ρg. In conservation form, ∂_t(ρv)+∇·(ρv⊗v+P𝟙)=ρg; pressure, density and thermodynamic closure must be supplied with initial/boundary data.
Values and equations
ρ(∂_tv+(v·∇)v)=−∇P+ρg; ∂_t(ρv)+∇·(ρv⊗v+P𝟙)=ρg
- ρ
- Mass density kg m⁻³
- v
- Fluid velocity m s⁻¹
- P
- Pressure Pa
- g
- Body force per unit mass m s⁻²
- t
- Time s
- 𝟙,⊗
- Identity tensor and tensor product
Conditions and scope
- Positive density, continuum local equilibrium and isotropic pressure stress; g is body force per unit mass and viscosity is neglected.
- No-penetration is the ideal-fluid wall condition; imposing viscous no-slip needs a viscous model. Incompressibility is an additional constraint, not built into this compressible equation. Shock solutions need conservation jump and entropy conditions beyond these smooth derivatives.
Sources · 1
References
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Evidence and review
Classical Mechanics III 8.09 (2014): Chapter 6, fluid mechanics: §6.1 material derivative equation 6.19; §6.2.1 mass balance 6.25–6.28; §6.2.2 pressure force and Euler equation 6.30–6.34. Conservation form follows product rule and the displayed continuity equation.
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