This person is extremely good in teaching. I never understood all these approximation and assumptions because I don't think my professor explained well. For the first time somebody here on RU-vid done a fantastic job. Need good teachers like this. I wish somebody would come on RU-vid and teach me Quantum Field theory in detail say following Pekin. Hats off to you. Give you 20 out 10 score . It gives me great joy when I see such good teachers.
Hi Brian, unfortunately I have to study my degree non-presential. Came to youtube as a desperate attempt to understand what boundary layer is about, as I continously failed in the trial to understand the old, anachronyc and expensive books that compose my guideline. You achieved to describe boundary layer concept in 30 minutes, you've saved me 3 hours of reading the ancient bibliography I'm supposed to read. BIG THANK YOU!
11:55 Hello sir, a great video first and foremost, but I couldn't help but wonder why the formula for the BL thickness doesn't say '5*x/Re' instead of '5/Re'. Surely this must be a small error, cause your BL thickness would be a dimensionless number, which a length scalar obviously isn't. Thank you for the helpful video
If I would plot the Hight of the boundary Layer in a laminar flow. My result is a function y = cte/sqrt(x). I used your formulas @ 13:12. But the function need to be y = cte*sqrt(x). Did I make a mistake?
Ah. I made a mistake. Thanks for noticing this. The formula I wrote, delta = 5/sqrt(Re) does not have correct units if delta is the height of the boundary layer. The formula should be delta/x = 5/sqrt(Re), now both sides are dimensionless. When you plot delta, not you get delta grows with the sqrt of x. Thanks for noticing and I'll try to make an annotation in the video to correct this.
RU-vid used to allow you to post annotations after a video was live that allowed me to fix little typos like this. They have discontinued that feature. I'll have to see if I can find another way to add the correction.
I am not sure there is a relevant mean value in a boundary layer, since the thickness evolves with distance down the plate. Can you elaborate your question a little more. Also, look up the "von Karman momentum integral" - that may address some what is underlying your question.
The 5 comes from an analytical solution to this problem (which I don't cover here) called the Blasius solution. You can find some resources online that describe this solution. The factor of 5 is not an exact factor that comes from this solution, but you are left numerically evaluating some factor and it turns out to be pretty close to 5. If you google Blasius solution, you can find more detail
