where D D t is the material derivative. ν ν = μ μ ρ ρ is the shear kinematic viscosity and ξ ξ = ζ ζ ρ ρ is the bulk kinematic viscosity. The left-hand side changes in the conservation form of the Navier–Stokes momentum equation. By bringing the operator on the flow velocity on the left side, on also has: