scott@aa.washington.eduOffice: 101 Kirsten Wind Tunnel Building
He certainly has a credible location. Means I'm going to have to be reeeeeal certain about the email I'm going to send him about the Coanda effect.
The two approaches, Newtonian and pressure
must be compatible. They're both based on physical laws. That's the fallacy that I was getting at with the Coanda/F=ma argument. In all the presentations of that argument that I've seen, there is a lack of connection between all the downward deflected air and the wing itself. Then viscosity and "stickiness" gets brought into it as to how flow stays
attached and, personally, I don't think that pans out, either. First, viscosity leads to boundary layers and boundary layers lead to separation. As for "stickiness," as opposed to a solid, a fluid, in and of itself -- the special case of surface tension excepted -- cannot support a load in tension or compression. It's like pushing a rope cut into 10 pieces. But surround that fluid that you are trying to apply a force to with a pressurized fluid of a same or different type and now it can support a load.
Worse, I'm going to go out on a limb, although I believe it's a short, sturdy limb and say that Eberhardt and the How Planes Don't Fly article are wrong in their description of the Coanda effect. If Coanda is viscosity/boundary layer driven, then the flow slows down, the bondary layer thickens and the flow separates and it sure doesn't seem like it would help in keeping flow attached on a nearly stalled wing! I'm going to have to ponder this one, but I suspect that in the water over the glass scenario, the flow leaves the faucet at atmospheric pressure, continues to
accelerate down the glass due to gravity, decreasing its pressure to below atmospheric and the surrounding air pressure holds the stream against the glass until the boundary layer slows the flow too much and the stream separates from the glass. The water's surface tension would help keep the water attached to the glass, but surface tension sure doesn't have a role in the rotarless helicopter or the blown boundary layer referenced above. I'm not 100% percent on it, but I'd be willing to put money down on a claim that the water-jet-on-a-glass Coanda effect would not work nearly as well, if at all, on the space station.
Supernatural beings like fairies?
And since I'm disparaging other people's credentials and criticizing credentialed experts, I suppose I should toss my credentials into the mix. I have an MS in mechanical engineering, have been working in hydrodynamics for about 15 years and have designed and analyzed about 15 underwater vehicles of various types and speeds.
