= Blasius equation
{c}
{title2=$f'''+\tfrac12ff''=0$}
For a steady incompressible <viscous boundary layer> over a flat plate with constant outer speed $U$, the <stream function> $\psi=\sqrt{\nu Ux}\,f(y\sqrt{U/(\nu x)})$ reduces the <Prandtl boundary-layer equation> to the displayed ordinary differential equation. The wall and outer conditions are $f(0)=f'(0)=0$ and $f'(\infty)=1$. The wall shear is $\rho U\sqrt{\nu U/x}\,f''(0)$, so its integral on one plate face of length $L$ is $2\rho U^2Lf''(0)/\sqrt{UL/\nu}$. Both equally exposed faces contribute twice this value.
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