Research bumps up aerodynamics

Tiny regular bumps applied to the wing of an aeroplane can substantially reduce total air resistance, and thereby the consumption of fuel.

Wind tunnel tests at the Royal Institute of Technology (KTH) in Stockholm, Sweden, have shown that small cylindrical bumps on a surface delay the transition from laminar flow (well-ordered) to turbulent (chaotic) when air flows over it, a crucial factor in total air resistance.

If proven outside the lab, this research could lead to savings for the air industry and lessen the environmental impact of increasing demand for air travel.

“The discovery is revolutionary for physicists working with fluid mechanics, since it goes against the conventional thinking that an uneven surface could only speed up the transition to turbulence,” said Jens Fransson, one of the scientists in the research group.

The new method prevents turbulence before it starts, unlike previous methods for reducing total air resistance which involved the elimination of turbulence that has already occurred.

In wind tunnel experiments at the Department of Mechanics at KTH, the scientists created velocity variations against the direction of the flow by placing tiny cylindrical elements on a surface. This hinders the occurrence of instabilities and delays the transition of laminar flow to turbulence.