Question

The thickness of the laminar boundary layer on a flat plate at a point A is 2 cm and at a point B, 1 m downstream of A, is 3 cm. What is the distance of A from the leading edge of the plate?

• A. 0.50 m
• B. 0.80 m
• C. 1.00 m
• D. 1.25 m

Answer 1

The correct option is B 0.80 m

Laminar boundary layer thickness,
$\delta =5\times \sqrt{\frac{xv}{V}}$
$\frac{{\delta }_A}{{\delta }_B}=\sqrt{\frac{x_A}{x_B}}$
$\Rightarrow \frac{2}{3}=\sqrt{\frac{x_A}{x_A+1}}$
$\Rightarrow \frac{4}{9}=\frac{x_A}{x_A+1}$
$\Rightarrow 5x_A=4$
$\Rightarrow x_A=0.8m$