Vortex Edge
Introduced in January of 2001, the Vortex Edge and tip profile incorporate two features intended to improve blade efficiency during the first half of the drive. Specifically, the Vortex Edge enhances the "dynamic effect," which dominates the first two phases of the stroke.
- The raised features on the back surface of the tip are "vortex generators" which act on the layer of water near the surface of the blade to decrease drag and increase lift.
- The blade perimeter tapers towards the tip to promote vortex development along the blade edges increasing the work done by the back surface of the blade as the angle of attack increases during the second phase of the drive.
An added feature of the Vortex Edge is that it protects the edge of the blade, preventing damage from wear or impact.
Testing of the Vortex Edge done during its development at Concept2, and controlled tests done outside of Concept2, have shown a speed advantage. The Vortex Edge comes standard on the Fat2 and can be ordered with the Smoothie or the Big Blade.
How the Vortex Edge Works
Testing at Concept2 has shown a speed advantage using the Vortex Edge, though more testing needs to be done to confirm its universal benefit. To date there has been no negative result in terms of speed or handling.
The dynamic effect or “lift” is generated by the water flowing around and along the blade. The longer the water flows around the blade without separating (breaking away), the longer the lift will be generated. Separation tends to occur as the angle of attack increases—in other words, as the angle between the movement of the blade and the flow of the water gets larger. This is exactly what happens in the 2nd phase of the stroke, as the blade moves away from the hull. By adding vortex generators to the back edge of the blade tip, we are able to postpone this separation as the angle of attack increases during the later stages of phase 1 and early in phase 2.
Example: Spoon under Faucet
This can be demonstrated using an oar blade under a faucet.
Photo A
The water stream is displaced by the “sticky spoon” effect at this angle of attack. Water is being moved back towards the starting line.
Photo B
At this angle of attack the water stream is losing contact with the blade. We are losing the “sticky spoon” effect at this point of the stroke.
Photo C
The water stream is still being displaced—being moved back towards the starting line—by the “sticky spoon” effect—even at the greater angle of attack. The effect is stronger and holds through more of the stroke.
Example: Aircraft Wings
The diagram at right is from an article at www.avweb.com (view article) that describes how vortex generators (VGs) on airplane wings can reduce drag and increase lift as the angle of attack increases.
Example: A Whale's Fins
The dynamic effect is also found in nature. Consider the fins of a humpback whale: vortex generators are found on the underside of the fin. In the last few years, scientists have been studying these features and have found that they allow the fin to create lift at a higher angle of attack than is possible with a smooth fin. It appears that these features have evolved over time, because they give the whales an advantage in terms of more powerful swimming and better maneuverability to catch the small fish on which they feed. This technology is now being applied to fans and windmill blades to improve efficiency.
The Delta Wing Effect
Again looking at aircraft technology we see that aircraft designed to fly at the higher angles of attack found in phase 2 use a delta wing. A wing or blade with tapered leading edges will form large vortices along the edges that will increase lift and decrease drag.