$8\mathrm{.}2$ It has been found experimentally that

$\frac{?}{\text{b}\text{a}\text{r}}(u)=(\frac{[{}_0]}{}{)}^{\frac{1}{2}}(\frac{y}{D}{)}^{\frac{1}{6}}$

where $D$ is the distance between two parallel planes. Give the expressions for $$ and Prandtl's mixing length $l$ as functions of $y.$