Timeline for Why does a fluid follow the wing?
Current License: CC BY-SA 4.0
12 events
| when toggle format | what | by | license | comment | |
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| Aug 16, 2021 at 21:41 | comment | added | Al Brown | Sounds good, yeah enough comments here. Have a good evening | |
| Aug 16, 2021 at 21:34 | comment | added | D. Halsey | @Al Brown I'm getting messages about avoiding extended discussions in comments, so I'm through commenting for now. | |
| Aug 16, 2021 at 21:32 | comment | added | D. Halsey | @Al Brown Inviscid calculations can have lift because they include circulation, but in real life, that circulation arises from the vorticity in the boundary layer. | |
| Aug 16, 2021 at 20:50 | comment | added | Al Brown | Also, much aerodynamic analysis uses inviscid assumption. Remember that lift comes from the bernoulli equation unrelated to viscosity? Or are we over that and talking about drag still existing without viscosity? Drag comes from 1. Viscous sheer and 2. Impinging gas. The former is greater but the latter is non-zero and contributes to drag. As we’ve seen, the reason it’s relatively low usually is that the molecules are moving fast relative to the object | |
| Aug 16, 2021 at 20:41 | comment | added | Al Brown | Ok I agree with that. Also, pressure is the name for moving molecules exerting force on a surface or on neighboring regions of the gas. If they weren’t moving on their own (apart from the average airflow), then they wouldn’t fill the backside of a moving wing because there wouldnt be a pressure difference to drive them there because thats what pressure is. That explains for example the increase in pressure with increasing temperature. The molecules moving faster (temperature) makes more pressure. | |
| Aug 16, 2021 at 15:15 | comment | added | D. Halsey | @Al Brown Molecules colliding with the surface just means there is pressure. None of the theories dispute that. | |
| Aug 16, 2021 at 14:52 | comment | added | D. Halsey | @Al Brown Sorry, but that's just wrong. The link you give seems to be someone's personal opinion. | |
| Aug 16, 2021 at 14:26 | comment | added | Al Brown | Secondly, “Without viscosity, airfoils would have no lift or drag (in 2D, at least).” is not true for either, incl 2-D. It’s especially far off for lift.. Bernoulli lift is unrelated to viscosity. Even for drag, the d'Alembert's paradox was shown hundreds of years ago to be off: “However, this view neglects the fact that even if the gas molecules do not interact with each other (i.e. if the gas is inviscid), they still collide with the object, which must result in a change of momentum and energy.“ from physicsmyths.org.uk/drag.htm | |
| Aug 16, 2021 at 14:19 | comment | added | D. Halsey | @Al Brown The boundary layer is directly responsible for creating the vorticity that perturbs the flow and allows it to follow the surface of the wing. | |
| Aug 16, 2021 at 14:16 | comment | added | Al Brown | The point of the boundary layer is only the assumption that the velocity of the surface matches the velocity of gas at the surface. It only “sticks” in the direction of the surface’s velocity, which is all viscosity can do because it only provides force in response to velocity. Viscosity does not provide any forces or sticking power in a direction perpendicular to the surface. So it doesn’t explain at all what makes the gas go to the surface against the gas’ momentum, which is the question. In particular there is no surface region of higher concentration. | |
| Aug 13, 2021 at 15:23 | history | edited | D. Halsey | CC BY-SA 4.0 |
added 361 characters in body
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| Aug 12, 2021 at 17:16 | history | answered | D. Halsey | CC BY-SA 4.0 |