Question

A flat with a sharp leading edge is placed along a free stream of fluid flow. Local Reynolds number at 3 cm from the leading edge is ${10}^5$. What is the thickness of the boundary layer?

• A. 0.47 mm
• B. 0.35 mm
• C. 0.23 mm
• D. 0.12 mm

Answer 1

The correct option is A 0.47 mm

Since the Reynolds number is less than 5 $\times {10}^5$, the boundary layer is laminar. The thickness of the laminar boundary layer may be given by the Blasius' equation i.e.
$\delta =\frac{5x}{\sqrt{R{e}_x}}=\frac{5\times 3\times 10}{\sqrt{{10}^5}}\Rightarrow \delta =0.47mm$