Tubercle effect

[1][2][dubious – discuss][citation needed] The tubercle effect works by channeling flow over the airfoil into more narrow streams, creating higher velocities.

Using computational modeling, it was determined that the presence of tubercles produces a delay in the angle of attack until stall, thereby increasing maximum lift and decreasing drag.

[1] The tiny hooklets on the fore edge of an owl's wing have a similar effect that contributes to its aerodynamic manoeuvrability and stealth.

[5] Researchers were motivated by these positive results to apply these concepts to aircraft wings as well as industrial and wind turbines.

Localized upwash is associated with higher angles of attack, which relates to increased lift, as the flow separation occurs in the troughs and stays there.

[7] The vortex created by the tubercle delays flow separation toward the trailing edge of the wing, thus reducing the effects of drag.

Cavitation occurs in areas of high flow velocity and low pressure, such as the trough of a tubercled structure.

[2] The tubercles on the flippers help to maintain lift, preventing stall, and decreasing the drag coefficient during turning maneuvers.

However, in practical application, turbines often operate at off-design conditions where stall occurs, causing a decrease in performance and efficiency.

[1][5] In order to look for possible improvement of the energy efficiency of turbine, the influence of leading edge tubercles must be investigated in more depth.

While these effects are found in many aquatic animals and birds, scaling these designs up to industrial application brings forward another set of issues regarding the high stresses associated by machinery.

In airplanes for example, designs are much more limited than the complex kinematics and structures of the joints in the wings of birds which produces agile turning maneuvers.

The utility of tubercle in performance improvement of engineering systems comes directly from examination of biological structures.