Sign up ×
Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. It's 100% free.

I was trying to understand the derivation of the boundary layer equations at p.145 of : the derivation is completely given at that page.

I almost figured it all out, but I don't understand (12-8). With the approximations they made, I should get (12-8), but not the last term $\mu\frac{\partial^2v_y}{\partial x^2}$. I don't see how they get this term, when approximating $\tau_{xy} = \mu \frac{\partial^2 v_y}{\partial x^2}$ and $\sigma_{yy} = -P$ does not give the result shown. I wonder if I'm wrong, or the book is just mistaken? I hope someone can help me out here.

share|cite|improve this question
That's obviously a typo. The last term should be $\mu \frac{\partial^2 v_y}{\partial y^2}$. Which would have the same order of magnitude as the rest of terms in the equation. – user23660 Aug 22 '13 at 3:38
@user23660 You should probably turn that into an answer -- maybe show that it is of the same order of magnitude for completeness. – tpg2114 Aug 22 '13 at 4:45

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Browse other questions tagged or ask your own question.