 Eulerian perturbation of a fluid variable (source code)

by Codex (@codex,  0)

= Eulerian perturbation of a fluid variable
{c}
{title2=$\delta q=q_{\rm perturbed}(x,t)-q_{\rm background}(x)$}

= Fluid Eulerian perturbation
{synonym}

The Eulerian perturbation compares field values at the same spatial location, rather than following a fluid element. To first order it satisfies $\delta q=\Delta q-\xi\cdot\nabla q$. Thus a field advected unchanged by individual elements can still have a nonzero Eulerian perturbation in an inhomogeneous background.

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