Navier-Stokes 方程

\frac{\partial (ρ U)}{\partial t} + \nabla \cdot (ρ U U) = - \nabla p + \nabla \cdot (μ (\nabla U) + {(\nabla U)}^{T}) - \frac{2}{3} μ (\nabla \cdot U) I + ρ g + S

;