= Quasi-steady Stokes approximation
{title2=$\mathrm{Re}\ll1,\quad L^2/(\nu T)\ll1$}
Neglecting both <convective acceleration> and local <acceleration> in the <Navier-Stokes equation> requires a small <Reynolds number> and an imposed evolution time $T$ long compared with the <viscous diffusion time> $L^2/\nu$. A slowly changing configuration may then be modeled by a sequence of steady <Stokes flows>. Rapid small-amplitude forcing can have small <Reynolds number> while requiring the <Unsteady Stokes equation> instead.
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