In simulations, phononic structures broaden turbulence control

At 640 mph, a passenger jet’s wings are being battered by wind and boundary-layer turbulence. In two new papers, Mahmoud I. Hussein’s team at the University of Colorado Boulder reports computational methods for shaping the microscopic vibrations beneath an aircraft surface, with the aim of controlling airflow without reshaping the wing or fuselage.

The approach uses phononic subsurfaces, or PSubs: engineered materials beneath a surface that passively manipulate vibrations where the surface meets a fluid flow. Earlier PSubs were designed to work at a single frequency. By coiling the phononic structures, Hussein’s team says it can produce “super-resonance,” extending the response across a range of frequencies, closer to the broad mix generated by real turbulence.

The second result tackles distance. Instead of placing one PSub at one location, researchers can arrange groups in a grid or lattice. The team calls the effect “scatterless interference”: it delays the downstream development of turbulence across a large surface, such as an aircraft wing or the body of a hypersonic vehicle.

The concrete payoff is fuel economy. Commercial planes consume more than 10,000 gallons of jet fuel on a single cross-country trip, and the researchers say improved fuel economy could bring major savings for airlines. The same ideas may extend to marine vessels, pipelines and turbomachinery, although the current work is focused on aerospace structures.

The boundary is clear: these results are still computational. Several groups have built functional physical prototypes and are working toward wind-tunnel demonstrations, but no effectiveness result from a flying aircraft is reported here. Adam Harris, a materials science and engineering doctoral student and co-author of both papers, describes the two techniques as complementary steps toward the versatility needed in real-world flow environments.