‘Virtual chimney’ for airports could improve local air quality

Simple fences constructed near airports could help shield nearby residents from pollution by funnelling emissions upwards, new research shows.

Researchers from several UK universities have demonstrated that fences known as baffles (a term describing structures that redirect fluids) constructed out of low-cost agricultural windbreak netting on lightweight frames could act as a ‘virtual chimney’.

‘Airfield surfaces are typically covered with grass, over which the wind can blow freely,’ said project lead Dr Mike Bennett of Manchester Metropolitan University, in a statement.

‘An array of baffles makes the surface rough in an aerodynamic sense. This sucks the momentum out of the exhaust jet, allowing its natural buoyancy to come into play. By suitably angling the baffles, we can also give the exhaust an upwards push, encouraging it to rise away from the ground.

The researchers, which included members from Cambridge, Cranfield and Southampton universities, successfully tested an array of three rows of baffles angled between 40° and 60° in order to optimise the vertical flow and ensure they didn’t blow over.

‘Although the exhaust will still disperse to the ground eventually, it will do so at a lower concentration,’ added Bennett. ‘We might hope to see a reduction in surface concentrations of around 50 per cent at the perimeter fence behind the place where aircraft are taking off.’

The baffles are titled at angles of between 40 and 60 degrees to give redirect the emissions while not being at risk of falling over.

The test baffles were only designed to be temporary prototypes so a permanent installation may look very different. Each one had to be robust enough to withstand the 80–90-knot blast from a jet engine, but flimsy enough to collapse harmlessly if an aircraft were to hit it.

The prototypes were less than the height of a person and around 2m wide but permanent fences could be much narrower, although a full-scale installation would need an area of around 1,000m2 behind a runway to be fully effective.

The tests also showed that the baffles reduced engine noise and jet blast on the airport perimeter.

‘There’s no reason why baffles couldn’t start to be installed at airports within two or three years,’ said Bennett. ‘From the point of view of local air quality, they represent a quick, cheap supplement to developing low-NOx [nitrogen oxides] jet engines.’

The project was funded through the EPSRC’s Airport Energy Technologies Network (AETN).