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Can anybody explain to me the Coandă effect well? I am finding that many definitions and explanations conflict.

I am particularly confused about the following points regarding the Coandă effect:

  • whether the Coandă effect is the same as normal boundary layer attachment to a surface
  • whether the Coandă effect is only defined for convex surfaces over which a jet (of the same state as the surrounding fluid) is tangentially blown
  • what causes the Coandă effect: the jet entraining the ambient fluid or a balance of pressure and centrifugal forces, or something else?
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Try this terrific site. It discusses the Coandă effect and how it is different from the usual process by which wings produce lift. –  Mike Dunlavey Jun 4 '13 at 12:45
    
The site wasn't technical enough, but thanks anyway. It also uses the "spoon under running water" example which I thought was dominated by surface tension rather than the Coanda effect. –  Flow Jun 5 '13 at 6:31
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1 Answer

The Coanda Effect occurs rarely in nature. It always involves a fast jet sheet. Such a jet may occur under a roof gutter for example if it is sloping so the water sheet can pick up some speed. It occurs at the underside of the inside top of the stomach after a drink because the falling water becomes a jet sheet and will flow under a surface adhereing to it. It is almost always man made.

NASA and others have been using it to increase lift up to 3 times by blowing a jet sheet from a slot to over a bluff trailing edge. This shifts the rear stagnation point to the underside and postpones stall.See "The Coanda Effect And Lift" at www.newfluidtechnology.com

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