Non flush rivets creating vortex

[Alan Fox]

All this talk about vortex generators is making me think that perhaps the rivet heads protruding on the leading edge of some aircraft could create turbulence , thereby increasing laminar flow........Any thoughts ???

[chrisk]

I suspect the rivet heads make horizontal rotors and the VGs make vertical rotors.  I'm going to guess only one type increases laminar flow...  However I am an electrical engineer, so this is a WAG.

[N201MKTurbo]

The rivet heads are in the boundary layer. they don't do anything.

[ArtVandelay]

The rivet heads are in the boundary layer. they don't do anything.

They do if they are on the leading part of the wing, where the boundary layer doesn't exist, or is very thin, it increases as it flows over the wing.

[smccray]

Paging KSMooniac...

[jetdriven]

Once the boundary layer trips that's the end of laminar flow in that region. Skin imperfections, chipped paint, even dead bugs trip the laminar flow. Rivets really ruin it. If they are all in a row, such as a rib, the effect is much less pronounced than if they run transverse such as along a stringer.

But it's not jst the loss of laminar flow, non-flush rivets create drag.

[Alan Fox]

If they are in the boundary layer and do nothing , than why would they be flush riveted on some planes?

[jetdriven]

The rivets after the spar on a mooney are buried in the turbulent boundary layer. The laminar flow boundary layer near the front of the wing is very thin. Even when tripped it's still pretty thin.

[KSMooniac]

Byron is correct.  Flush rivets make sense on a laminar flow wing, like our Mooneys, but even on a laminar section the boundary layer will eventually transition to a turbulent boundary layer on it's own (and thus get bigger and draggier), so putting protruding rivets "back there" makes economic sense since flush doesn't buy any more performance.  (it does look great, though!)  Planes with non-laminar wings (like a 172) will get very little benefit from flush rivets.

 

The VG's work by creating a pronounced vortex (duh!) that stays attached at higher angles of attack due to the higher energy of the flow.  A "regular" boundary layer will separate easier/sooner at higher angles of attack, and thus stall sooner.  I doubt any disturbance produced by a protruding rivets adds energy to the flow...probably just drag.

[Guest]

I remember hearing a story about the designers of the Spitfire who were said to have glued split peas to the flush rivets in an effort to determine where the trade off was in drag to labour cost was.

Clarence