Integral momentum-flux balance for a two-dimensional plume (source code)

= Integral momentum-flux balance for a two-dimensional plume

For a steady incompressible plume with localized vertical body force $b(x)\delta(y)$, decay of velocity and shear at transverse infinity gives
$$
\frac{d}{dx}\int_{-\infty}^{\infty}\rho u^2\,dy=b(x).
$$