Acoustic Reduction of Flow Separation

Airfoils produce more lift and less drag when the boundary layer is attached to the airfoil. With most aircraft there are combinations of airspeed and angle of attack where the boundary layer at least partially detaches from the airfoil. Reducing boundary layer detachment increases lift and reduce drag reducing fuel consumption and improving control for the pilot. Two methods known to improve boundary layer attachment are heating the air and supplying acoustic pressure at an airfoil dependent frequency. In Phase I we demonstrated that thin (<50 µm) ribbons made from carbon nanotubes can be used to produce heating elements which can be heated and cooled hundreds of times per second. When properly located on the surface of a wing they can maximize boundary attachment as demonstrated by improvements of up to 20% in lift. In Phase II we will improve our understanding of the function of these thermoacoustic elements and demonstrate their durability and their effectiveness with larger components. In Phase I we demonstrated multifrequency sound generation on surfaces in a wind tunnel using nanotube heating elements, and achieving improved lift and TRL 3. Phase II will include medium scale wind tunnel tests verifying the effects and achieving TRL 5.

Developing and dispersing this technology will be of greatest benefit outside of NASA, with improved safety and profitability for commercial aircraft operators at all levels, from private pilots to commercial airlines. By increasing lift and reducing drag on airfoils the technology being developed here, if implemented, can reduce fuel consumption, increase payload, or produce a combination of both. Any of these choices will make aircraft operation more profitable. (Fuel is second only to salaries as an airline operating cost.) Reducing fuel consumption will also reduce emissions, including aircraft-produced CO2. Reduced boundary layer separation will also improve the effectiveness of control systems. Making an aircraft more responsive to its controls, an added advantage, will make a small contribution to improved safety as well. Beyond these direct applications, this technology offers the promise of improved aircraft deicing systems as the same heating elements are used to loosen and shed ice formed in flight, and even further afield, lead to thin layer speakers that can be located in places where it is not now possible to locate speakers.

One of NASA's functions is to develop cutting edge technology for adoption by the civilian and military aviation sectors, technology like the technology in this project. This can keep the U.S. aircraft industry on top. The technology proposed here is funded under subtopic A2.07 Flight and Propulsion Control and Dynamics under Fundamental Aeronautics. NASA operates its own fleet of transport aircraft to move people, spacecraft, and rocket components around the country and around the world. Adding this system for reducing flow separation to those aircraft could increase carrying capacity and reduce fuel consumption.

This is early/mid-stage (TRL 5) — the most realistic path in is NASA SBIR/STTR, which funds small businesses and research institutions to develop technology aligned with NASA's needs (equity-free, phased funding). Check whether a current SBIR/STTR solicitation topic overlaps with this project's technology area, or contact the project directly (above) to ask.

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