Friction drag could be cut by 40% with aircraft surfaces that have small cavities with shaped orifices to affect turbulence mechanisms, say researchers.

The orifices would be designed to direct oscillated air across the aircraft's surface perpendicular to the relative wind. It is this redirected air flow that is believed to affect near-wall turbulence mechanisms and reduce friction drag.

Air flows into the orifice and its cavity beneath and the pressure increases within the cavity which then forces the air out. The expelled air then reduces the cavity pressure allowing more air in, and this oscillation process continues.

The project's leader, University of Warwick fluid-solid mechanics associate professor Duncan Lockerby, says: "This is for a fully turbulent boundary layer. We are pushing ahead with prototypes and have a separate three-year project to look more carefully at the physics behind it."

Friction and interference are the two causes of drag. By halving drag with this reduction in skin friction Lockerby's researchers expect a proportional reduction in fuel burn, which would be 20% of the aircraft's total.

He added that working back from the Advisory Council for Aeronautics Research in Europe (ACARE) noise and emission reductions target date of 2020 Airbus would like to flight test the technology in 2012 to realise its benefits by the ACARE deadline. EADS Innovation Works is contributing funds to the project.

The ACARE targets are a 50% reduction in fuel burn, percieved noise and carbon dioxide emissions with an 80% reduction in nitrogen oxides output.

With £376,000 ($595,000) provided by the UK's Engineering and Physical Sciences Research Council and additional monies from EADS, the project is being carried out by researchers at the universities of Cardiff, Imperial, Sheffield and Queen's in Belfast.

Source: Flight International