Question

In a laminar boundary layer, the velocity distribution can be assumed to be given, in usual notations, as
$\frac{u}{v}=\frac{y}{\delta }$
Which one of the following is the correct experession for the displacement thickness $\left({\delta }^{\ast }\right)$ for this boundary layer?

• A. $({\delta }^{\ast }=\delta )$
• B. $({\delta }^{\ast }=\delta /2)$
• C. $({\delta }^{\ast }=\delta /4)$
• D. $({\delta }^{\ast }=\delta /6)$

Answer 1

The correct option is B $({\delta }^{\ast }=\delta /2)$

${\delta }^{\ast }=\int (1-\frac{u}{v})dy=\delta {\int }_0^1(1-\eta )d\eta Where\eta =y/\delta {\delta }^{\ast }=\delta /2$