Planes often use vortex generators to cause the air flow to 'stick' to the wings a little longer than it normally would. I've just finished an older book that talked about a similar thing being done with sails, this by burning short rows of small holes in the sails so as to create these vortexes and thus prevent airflow breakaway as it approaches the leech. Does anyone know what became of this research. And no, I'm not going to start burning holes in my perfectly good sails until I know a LOT more about this than I do right now !.
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vortex generators
vortex generators on airplanes, which are used only to keep the flow laminar over the ailerons, are small metal airfoils perpendicular to the surface of the wing. how would you mount such a thing on a sail, or why?
vortex generators on airplanes, which are used only to keep the flow laminar over the ailerons, are small metal airfoils perpendicular to the surface of the wing. how would you mount such a thing on a sail, or why?
VG's on Hulls
Back in the '80's, one of the America's Cup teams worked with Boeing and 3M to figure out where to place Vortex Generators (VG's) on the hull, fin and rudder of their entry. As mentioned in previous posts, the idea behind VG's is to keep the fluid (either air in the case of an aircraft, or water in the case of a, well, you get the idea...) "attached" to the surface longer, creating more lift and/or reducing drag from disturbed flow. 3M had a tape product that created little "ribblets" that could be stategically placed on areas of the hull, fin and rudder that could benefit from increased attachment - to increase the lift generated by a fin or rudder, or to decrease the drag introduced by disturbed flow. Boeing has the advanced CFD (computational fluid dynamics) resources to analyze the vessel and model the interaction with the fluids/water. Voila, winning combination. The link will give you some more exposure to the use of VG's on small aircraft. Good Luck! Tim Brogan April IV C350 #68 Seattle
Back in the '80's, one of the America's Cup teams worked with Boeing and 3M to figure out where to place Vortex Generators (VG's) on the hull, fin and rudder of their entry. As mentioned in previous posts, the idea behind VG's is to keep the fluid (either air in the case of an aircraft, or water in the case of a, well, you get the idea...) "attached" to the surface longer, creating more lift and/or reducing drag from disturbed flow. 3M had a tape product that created little "ribblets" that could be stategically placed on areas of the hull, fin and rudder that could benefit from increased attachment - to increase the lift generated by a fin or rudder, or to decrease the drag introduced by disturbed flow. Boeing has the advanced CFD (computational fluid dynamics) resources to analyze the vessel and model the interaction with the fluids/water. Voila, winning combination. The link will give you some more exposure to the use of VG's on small aircraft. Good Luck! Tim Brogan April IV C350 #68 Seattle
They also bubble generators on the waterline
These were to produce tiny bubbles at the waterline to decrease resistance of the interface between water and the hull. Interesting?
These were to produce tiny bubbles at the waterline to decrease resistance of the interface between water and the hull. Interesting?
Lifting or Planing strakes
That are what the small A shaped strakes from the bow aft are for on high-performance speed boats, and lesser ones too. Gets that water bubbling, so get on their plane much faster.
That are what the small A shaped strakes from the bow aft are for on high-performance speed boats, and lesser ones too. Gets that water bubbling, so get on their plane much faster.
Attached flow at leech ...
There is a big difference between the vortex generators the original post refers to and the boundary layer control of riblets etc. The separation at the leech (trailing edge of a wing) due to laminar separation just does not happen on cloth sails. When the main is eased until the leech tells steam, then hardened until the tells start to flick, there is a very small separation of a turbulent boundary layer. Easing the sheet just a big gets the tells flying again. If it was laminar separation, the tells would stream until the flow separated then most of the drive would be lost and the sail would have to be eased 5-10deg to get flow attached again. Cloth sails just don't support laminar flow, the seams and stitching trip the flow to turbulent long before gets to the leech. The riblets on Stars & Stripes in 1987 served to reduce the thickness of an already turbulent boundary layer. They did not make a laminar layer go turbulent. Where laminar flow exists, the surface cannot be too smooth. When the flow is turbulent some surface treatments can reduce the energy in the boundary layer and reduce drag. The grooves in Stars & Stripes' riblets were .007" deep, it didn't take much. The greatest benefit was in light air where the riblets took about one minute off the time for a 24 mile course. In a breeze, they figures the riblets were worth only about 15 seconds over 24 miles.
There is a big difference between the vortex generators the original post refers to and the boundary layer control of riblets etc. The separation at the leech (trailing edge of a wing) due to laminar separation just does not happen on cloth sails. When the main is eased until the leech tells steam, then hardened until the tells start to flick, there is a very small separation of a turbulent boundary layer. Easing the sheet just a big gets the tells flying again. If it was laminar separation, the tells would stream until the flow separated then most of the drive would be lost and the sail would have to be eased 5-10deg to get flow attached again. Cloth sails just don't support laminar flow, the seams and stitching trip the flow to turbulent long before gets to the leech. The riblets on Stars & Stripes in 1987 served to reduce the thickness of an already turbulent boundary layer. They did not make a laminar layer go turbulent. Where laminar flow exists, the surface cannot be too smooth. When the flow is turbulent some surface treatments can reduce the energy in the boundary layer and reduce drag. The grooves in Stars & Stripes' riblets were .007" deep, it didn't take much. The greatest benefit was in light air where the riblets took about one minute off the time for a 24 mile course. In a breeze, they figures the riblets were worth only about 15 seconds over 24 miles.
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