Undulations in the 3D profile of turbine blades reduce drag.

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Researchers with the Virtual Interchange for Nature-Inspired Exploration (VINE) at the NASA Glenn Research Center in Cleveland, Ohio, have created a turbine blade inspired by the shape of harbor seal whiskers. They describe their design in the paper, “Application of Pinniped Vibrissae to Aeropropulsion.” The prototype, called ‘Seal Blade’, shows drag reduction at all incidence angles compared to modern airfoil geometry while not sacrificing lift. The Seal Blade’s geometrical features are modeled after the wavy shape (undulations) of seal whiskers, which experience less drag than smooth-surfaced cylinders and ellipses. A key challenge for variable speed turbines is to operate at large ranges of angles and rotor speeds while still maintaining high turbine efficiency. At high incidence angles, fluid flow may become detached from the surface of the turbine blade, creating a wide region of disordered swirling fluid behind the blade (in its wake). This disordered wake increases drag on the turbine blade and impairs its performance, but currently, separation of flow is difficult to manage and many designs just accept it. The undulating profile of the Seal Blade’s leading edge alters the fluid flow over the blade, helping it to stay attached to the surface at high incidence angles. By reducing flow separation and maintaining a thinner, more ordered wake, researchers predict that the Seal Blade could reduce drag by up to 50%.

Biomimicry Story

To develop a new blade geometry that could improve turbine performance, the VIBE research team looked at how previous airfoil designs have been inspired by natural forms. The review covered a variety of organisms from marine animals like whales, harbor seals, and sharks, to flying animals like owls and dragonflies, to even plants like cacti and palm trees. A common theme among many of these examples is grooves and ribs on blades that can reduce drag under certain conditions. These natural forms and their fluid dynamic properties hold promising strategies that could help solve human challenges in aeropropulsion. The research team was particularly intrigued by the motion-sensitive whiskers of harbor seals that detect slight disturbances in fluid flow around them. Earlier research by Wolf Hanke et al. showed that the 3D shape of a harbor seal whisker reduces the drag force acting on it by 40%, compared to a smooth circular cylinder. The whiskers’ wavy shape does this by altering the flow behind the whiskers, reducing the forces normally associated with swirling fluid in a wake.  Using CT scanning, microscopy, and 3D scanning techniques, the VIBE team characterized the geometry of whiskers from different seal species. The team then used these measurements to design a modified power turbine blade with a 3D profile matching the wavy shape of seal whiskers.  The Seal Blade design was tested in both simulated computer models and wind tunnel experiments. In the future, the VIBE team plans to examine Seal Blade performance under additional conditions (varying 3D profile measurements, adding rotation and interactions with other turbine parts), and determine whether the blade’s altered wake leads to other benefits, such as reduced noise.

This page was contributed by Leon Wang (Research Assistant ASU Biomimicry Center).

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References

Journal article
Application of Pinniped Vibrissae to AeropropulsionASME Turbo Expo: Power for Land, Sea, and Air, 2A: V02AT38A023June 15, 2015
Shyam V, Ameri A, Poinsatte P, Thurman D, Wroblewski A, Snyder C ASME Turbo Expo 2015: Turbine Technical Conference and Exposition Volume 2A: Turbomachinery

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