$6\mathrm{.}2.$ The boundary layer profile on a curved surface is found to be well described by:

$\frac{U}{U_{}}=\frac{4}{b}ar(y)-\frac{6}{b}ar(y{)}^2+\frac{4}{b}ar(y{)}^3\frac{-}{b}ar(y{)}^4\frac{,}{b}ar(y)=\frac{y}{}$

by examining the form of the axial momentum equation at the wall $($i$.$e$.$ at $y=0),$ determine whether this boundary layer is growing in an adverse or favourable pressure gradient. Define also the relationship between the skin friction coefficient $C_f$ and the Reynolds number of the boundary layer $R{e}_5.($Answer: favourable, $C_f=\frac{8}{R}{e}_{}$; Tip: start from axial momentum equation$).$

QED