= Hiemenz flow
{c}
{title2=$f'''+ff''-(f')^2+1=0$}
The steady planar <stagnation point> <boundary layer> with outer <velocity> $(Ax,-Ay)$ has the <similarity solution> $u=Ax f'(\eta)$, $v=-\sqrt{A\nu}f(\eta)$, $\eta=y\sqrt{A/\nu}$. The <Prandtl boundary-layer equation> becomes $f'''+ff''-(f')^2+1=0$, with $f(0)=f'(0)=0$ and $f'(\infty)=1$. Its thickness is of order $\sqrt{\nu/A}$, independent of horizontal distance. Normal dynamic <pressure> corrections are of smaller order than the tangential driving <pressure>.
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