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I think so too!

Most welcome!

Aw thanks!

I'm not sure what you mean. Are you referring to the vortex initiated at the start of the flow---as in when the airfoil first accelerates?

@@prof.vanburen yes, exactly that

Do you mean generally how a foil might turn the flow downwards, producing the circulation that is the footprint of lift? Or how in reality the no-slip boundary leads to a boundary layer full of rotational flow?

@@prof.vanburen the latter. I think this validates the Kutta condition

Thank you for watching!

You're welcome, good luck in your studies!

Ah thank you so much!

My pleasure! I looked through the video again because I wanted to be sure, I am not sure where Cp (which is sometimes pressure coefficient) pops up, but I suspect you mean Cl instead, as in the lift coefficient? If so, I should say first that Cl does not *perfectly* stay the same at different scales. Other concepts like turbulence and Reynolds number come into play here. However, for the most part, it is sufficiently equal across a wide range of different scales. This is because take into account all the variables that impact lift when we scale the problem. A bigger airfoil would produce bigger force at the same air speed, but lift coefficient takes that into account by scaling with the area. Does this help at all? Otherwise, I think the text by Anderson might be helpful here. Otherwise, my video in fluid mechanics on non-dimensional numbers more completely goes over these concepts in a way that is not restricted to aerodynamics.

Thank you!

Hey hi , I'm also doing aerospace engineering ( first year) and the college starts July 10 . I'm more passionate to learn about space shuttles , and i want to self learn . Is you can suggest me on how to self learn ? Thanks a lot ❤

I am glad they helped!

@TITAN_2608 Rocket science! I am not sure of any good references in this specific area---it's not really my area of expertise. I know NASA has a ton of good online resources, that's probably where I would start.

@@prof.vanburen thanks a lot

Thanks for clarifying!

Thanks for clarifying!

Thank you, I really appreciate you going through the videos so closely and catching my (many) goofs!

Thanks, but we will have to agree to disagree on this one. While I think the folks at NASA can be brilliant, I have seen the explanation you are referring to you and I don't find their rebuttal of the idea complete. And I think that's okay, because this is a very hard problem that doesn't get a simple answer! If flow passes by curvature---like one wall with a hill or the leading edge of an airfoil---it needs to react. If things are slow, the fluid just entirely (up to effectively infinitely away from the surface) moves up and over the curve and it is happy. This does not lead to the Venturi effect which is generally used to explain contracting enclosed systems. However, if it is moving rapidly by this curvature, shifting upwards takes time, and the flow might not have that time to react due to compressibility. So, if it can't get out of the way in time (and conservation of mass needs to be obeyed otherwise the world explodes) the flow can can do things like increase in density or speed up in this 2D approximation. Why is speeding up not an option for mass conservation? Would this not be a "virtual" contraction, where the "top wall" of the Venturi is really just reaction time? I know NASA in that reference discusses the flat plate as evidence, but the flat plate also leads to flow fields with curved streamlines that behave like more curved surfaces. Also, it talks about the bottom-side of the airfoil but there curvature is not nearly as rapid. Furthermore, the speed up explanation in this video is specifically attributed to traditional airfoil shapes and is only a smaller part of the big picture. It is this effect in combination with the others that lead to the supreme lift of airfoils. I am not sure my explanation is any more convincing, but I also don't see where in the aeronautics series from NASA that they explain the acceleration of flow around the curvature at the top of the airfoil, which certainly happens. It seems that course online just leads to "Euler equations are complicated". Yes they are. I have seen other explanations that include consideration of angular velocity and centrifugal things, but they didn't resonate with me (or perhaps I just didn't understand them well enough). Anyway, thanks for getting me to think about it more deeply!

Haha I have a mathematically talented grad student who also won't let me live this down. You're very correct here...but it certainly looks like a chain rule 🤔

My pleasure!

My pleasure!

You're welcome!

It has been a while since I looked at this lecture! I think it is because earlier in the video we are considering generalized calculation of lift and drag from the upper and lower surfaces of generic shape. Further down, we consider just a cylinder which has simplified versions of the equations. I will have to re-watch in detail just to make sure that's the case.

This is a heavy question and I am happy it is more in my area of expertise! In this case, I think it would be more valuable to dive into journal articles and not books. While some books might exist, it's still a vastly growing area of our understanding and researchers first publish their findings in journals---which I think is where the coolest stuff is. One such journal you could look into is Bioinspiration and Biomimetics. Otherwise, I tend to try and follow the work of groups I am familiar with. For example, Prof. David Lentink has always been a go to for someone I check out to see where the state of the art is in bird-like drones. And, even if you don't have paid access to the journal, authors are usually more than happy to share a copy of their work for free if you just email and ask.

You're welcome!

That would be a cool vid!

Hey thanks!

Good luck with your thesis! What topic in fluids are you covering?

Aw thanks!

Glad it helped!

I think this translates roughly to "I don't understand"? Happy to help if you have any specific questions!

Hmm, good question. I haven't done it out the reverse way because I think you might lose important terms if you simplify at the beginning, but I'd have to check. Regardless, if you start with the RANS equations and eliminate from there, isn't it the same amount of terms to compute anyway?

Aw thanks! I am happy with everyone involved, regardless.

Thanks!

Thanks, I think!

Definitely the ethics of aerospace education and its inherent integration with human violence (WW1 and WW2 rapidly advanced the field) are something important to consider and discuss

@@prof.vanburen I can’t even understand this

Hmm, good question. I'm not sure it would appropriately capture the end effects as it will change things slightly (generally for the better with regards to induced drag). Potentially you might find measurements on induced drag of winglet systems in literature?

@@prof.vanburen It was hard to find an appropriate way to calculate the induced drag of winglets. What we eventually found is that by predicting the downwash profile of a wing (by for instance using computer programs like OpenVSP or XFLR5). An expression can be found for the circulation, resulting in an estimation of the induced drag (as explained in the video). We are however not sure if these estimates come close to the real world. Moreover, we found that using the method of restricted variations that the optimal induced drag is obtained when the downwash is proportional to the local cosine of the dihedral angle. So when having a winglet at for example 90 degrees dihedral, the net sidewash should equal 0. This means that the winglet should not produce thrust, however the winglet causes a upwash on the main wing, reducing the induced drag of the main wing. This way, the winglet mainly helps the main wing perform better, instead of producing thrust itself. Some more considerations can be found in our Aerodynamics Assignment for the University of Twente: dickdekker.jouwweb.nl/induced-drag-of-winglets

Aw thanks! Turbulence is one of my favorite subjects, I'm glad it resonated with you.

Thanks for your patience! Just getting to comments after a short stint away. This is a good question. In these cases, there are multiple velocity scales (tip speed vs forward speed) and it is very hard to preserve all the non-dimensional numbers when scaling down. If you scale down in size, usually you need to increase velocity to compensate. This means, needing much higher rotation angular velocities of the turbine (to preserve tip speed ratio), which introduces all different sorts of problems. Definitely a challenge! Tip velocity is just a lateral velocity component, there is still usually a forward velocity. Typically, you choose based on which one is dominant.

dot indicates "change in time", so it is just the symbolic definition of mass change of the cube.

Not sure where specifically you mean, but generally I draw pressure as being normal from the surface with the arrow length correlating to pressure strength.

Great question, I think I am just confusing with my arrows. In that case, it's really to indicate there is a strong pulling force (low pressure region)

@@prof.vanburen Your videos are great! For this point, I also got confused, since I would expect the top/bottom pressure to be lower, since the velocity is higher. Would it make sense to add a note about that? Thanks so much for your videos.

Glad to help!

Back to the basics! If I ever am asked to teach the course at Uni, I can get some video lectures for it.

Nice!

Really great question! I'm guessing it is just because it worked, we found that the skin friction scaled with flow gradient, which in this case is in the y-direction. There might be a more rigorous math reason, or a better explanation---in either case I do not know it.