er...'kay.
I've just skimmed the posts, and so will offer the following... feel free to move the response to jet blast if you want to.
we have had Bernoulli's theory rammed down our throats since time amoral, and immemorial... etc. like, forever!. The morality is that it still keeps being rammed and it just ain't so. We teach it, and we examine on it and it is a nice analogy but that is all it is.
The pressure distribution charts are valid, as are the pointy arrow thingies, but the problem is we have a massive disconfubulation (like a discombobulation but better!) as to the why. The FAA teaches that the air wants to get from A to B over the top, at the same time as the flow goes underneath from the same points. Why? Does air have a mind? Does it have evil intent? is air sentient? Add a slot, and start doing the maths on what the little air mites are gonna do next, it's enough to confuse the poor wee things. For the wing/propeller comparison, if one does, and one doesn't, then we be needin' parallel universes in the same few feet, which just ain't gonna do it. No sir, it just ain't so.
We also read we gotta have deux Kutta points to get le lift de großer Flügel, which is curious, cuz the last 35 years of experimenting on propellers was all about getting rid of the trailing edge Kutta condition, which massively reduces drag (except at low AOA) and gives the CLs a happy smile. So that seems at odds with actuality.
Next time at the sink, bath, basin or pool, grab a flat/curved/airfoil shape or your hand or tea spoon... knife or another kitchen utensil sans tines and translate it across the fluid (water/beer/milk/cappuccino... etc) at no angle of attack to the vector of movement. The fluid doesn't object, and it doesn't make determinations as to going uppity or downy, it just don't, not a bit. Now do it again, and this time do it at a slight angle to the vector of motion and guess what.......
At the point where it started to move there is a vortex formed, and it rotates in a direction as... the forward flow of the vortex is in the direction of the leading edge of the blade to its trailing edge.... the whole blade tries to move in the direction that the leading edge is relative to the trailing edge (spoons, talking about mean camber lines)
when the blade gets to the other end of the pond, stop the blade, and the point where the blade stops will generate another vortex off the leading edge... both the start and stop vortexes are opposite directions to the bound vortex that was developed by the flow around the spoon/knife, foil, cheese slice, etc. So we have just proved over coffee, (tea works well too... in fact better, as the tea leaves are pretty to watch move around... and you can tell the future by reading them too). The bound vortex has a circulation that is rearwards over the "upper" surface and forwards on the lower surface... for a blade moving right to left with a positive AOA, the flow is clockwise, and start and stop vortex are anticlockwise... (Fig Newton be praised...) Add the translation velocity to the vortex and you get the velocity profile, and then go get the maffs from sitting on Boyles. And that is yon pressure distribution. join happy dots or arrows normal to the surface and you get your answers. The nice thing is, it gives the correct answer for flows in Slats, flap gaps and for Flettners thingey, and tennis balls with spin, or Donald J's slice through the heart of the constitution.
Aerohydrodynamic lift arises from bound vortex structures, the wing is just a vortex device, as is the propeller, rotor, fan blade, compressor blade etc. Now in turbines, (termites?) when there is lots of separation going along, then the flow gets more fun, and a simple approximation comes out of impingement/reaction-flat plate geometric lift but it is still in fact vortex flow. around the blades. the wake is just that, the flow in the wake of the blade. Ion or chemical rockets are simple reaction to the impulse, but then the flow in a throat or around an expansion body is pretty interesting where there is happiness to be found in maintaining laminarity of the flow near the surface, to minimize thermal transfer to the structure and to minimize erosion.
All good fun, just like Bernoulli thought it would be.
...Of course, that also explains why fan jet engines lose efficiency at altitude when considering TSFC. It's almost like they are a FANCY FIXED PITCH PROPELLER.... what a shame that you can't change the flow around a fixed-pitch propeller... wait on, as 44 said, yes you can! And it is a lot easier than transwarp beaming...
...That's what I'm talking about! How do you think I wound up here? Had a little debate with my instructor on relativistic physics and how it pertains to subspace travel. He seemed to think that the range of transporting something like a... like a grapefruit was limited to about 100 miles. I told him that I could not only beam a grapefruit from one planet to the adjacent planet in the same system - which is easy, by the way - I could do it with a life form. So, I tested it out on Admiral Archer's prized beagle...
Wait, I know that dog. What happened to it?
I'll tell you when it reappears. Ahem. I don't know, I do feel guilty about that.
What really puts the Bernoullis in the balus ay wok wok is playing with supercritical sections, or sonic flow, then the poor little mites get all collywobbly and confused. Vortex flow still werks gladly. kind of.
Maski long planti toktok!
On barn doors...
- radius of the LE alters the shape of the CL/AOA curve around peak Cl...
- Camber shifts the A-slope upwards...
- TE thickness moves the slope like camber...
- T/C alters Cd/AOA...
- %MAC for max thickness alters Cd...
- % chord for max camber alters Cm...
For helicopters, none of the above means much once the blade starts to turn, dynamic pitch changes make everythang much more interesting, there is no clean smooth line of coefficient for a rotor if the inflow is not perfectly axisymmetrical.... they all look like
D,s
P's and lopsided and inverted
T's instead of pretty clean lines like you get to see in I'm an Abbott and a VonWanderedoff's [1] wonder book on Fairies of wing sections, which gets us back to Bernoulli.
PS: when you get to sit over the wing sometime, on yon jet transport Boeing/Bus/Embraer... etc and you have the sun aligned with the quarter chord, either away from the top or in the opposite direction, you will see the shockwave shadow, Herr
August Toepler's schlieren image like. you will note that for most wings, it's nowhere near where it should be. It sits far forward of where the flow modeling of a section would suggest it should, for conventional sections such as BAC 450, 451, 452 etc, or for supercritical such as SC(1)-0710 and similar Whitcomb style sections, [2] [3][4] [5], Eppler's 403 etc... Flying is fun.
[1] Abbott, I. H. & Von Doenhoff, A.E., (1959) "Theory of Wing Sections Including a Summary of airfoil Data",
Dover Publications, 1 Jan 1959
[2] Charles D. Harris, "NASA Supercritical Airfoils", NASA Technical Paper 2969, pp. 1-76.
[3] Richard T. Whitcomb, "REVIEW OF NASA SUPERCRITICAL AIRFOILS", National Aeronautics and Space Administration, Langley Research Center Hampton, Virginia pp. 1-17.
[4] K.Harish Kumar, CH.Kiran Kumar, T.Naveen Kumar, "CFD ANALYSIS OF RAE 2822 SUPERCRITICAL AIRFOIL AT TRANSONIC MACH SPEEDS", International Journal of Research in Engineering and Technology, Volume 04 Issue 09, September 2015, pp. 256-262
[5] Sana Kauser, Mr. Kumara Swamy, Dr. MSN Guptha "Aerodynamics Analysis Of Naca Sc (2) -0714 Supercritical Airfoil Using Computational Fluid Dynamics", International Journal of Scientific Research and Engineering Studies, 02 (06), June 2015, pp. 38-41.