9.67 Small wind tunnels in an undergraduate laboratory have $305-\mathrm{mm}$ square test sections. Measurements show the boundary layers on the tunnel walls are fully turbulent and well represented by $\frac{1}{7}$ power profiles. At cross section ( 1 ) with freestream speed $U_{1}=26.1 \mathrm{m} / \mathrm{s},$ data show that $\delta_{1}=12.2$ $\mathrm{mm} ;$ at section (2), located downstream, $\delta_{2}=16.6 \mathrm{mm}$ Evaluate the change in static pressure between sections (1) and (2). Estimate the distance between the two sections.
