Consider a steady, and incompressible flow over a body with characteristic length $\text{L}$. The boundary layer thickenss at a distance $x$ from the leading edge is $\delta$. Which one of the following assumptions is correct for deriving the prandtl boundary layer equations?
- $\delta \approx L$
- $\delta>L$
- $\delta \gg L$
- $\delta \ll L$
