Thread: Question Holes in wings for boundary layer blowing? View Single Post
Jan 21, 2011, 11:15 AM
Joined Aug 2006
2,269 Posts
Quote:
 Originally Posted by JaRaMW As I see it, a slat is arranged in such a way that it blows high energy air to the upper surface's boundary layer. However, I remember a paper from a sailor (?) who stated that's not entirely true, the slat being a small wing in front of the main wing that alters the total circulation in a more favourable way. Supposedly foresails on sailboats are similar to slats.
Sounds like you've read one of Arvel Gentry's articles. He's not a sailor he's a retired aeronautical engineer and a yachtsman (sailor is a job yachtsman is a hobby).

Quote:
 The gap between slat and wing needs to be of considerable size so that enough air can flow through, otherwise the kinetic energy would be too low to have any useful effect.
The slot must be wider than the thickness of the boundary layers of both surfaces. That's not necessarily a lot

Quote:
 A line of holes would not allow a flow anywhere as strong unless the holes were quite large. Furthermore the exit direction of the air on the upper side would not be parallel to the surface unlike the flow from a slat.
There has been considerable confusion between two entirely different use's of blowing in this thread. My reading of post #1 lead me to believe that he was asking about blowing little jets vertically from the upper surface to act as turbulators. These little jets are perpendicular to the airstream and only have to blow through the boundary layer plus a millimeter or two so the pressure inside the wing doesn't have to be very high. This system requires either a pump or an air scoop below the wing to pressurize a plenum inside the wing. It is not in any way similar to a blown flap which requires a significant volume of high pressure air blowing tangentially to the surface.

Quote:
 My guess is that the air that passes through such a line of holes rather works as a turbulator, simply tripping the BL into a turbulent state rather than directly increasing its kinetic energy.
Bingo

--Norm

BTW holes are listed as item "F" in this group of aerodynamic bandades
Last edited by nmasters; Jan 21, 2011 at 11:27 AM.