When small mammals venture out at night they're in danger of becoming prey to owls that swoop in silence and with great precision. But how do owls achieve this, and what can engineers learn from them?
PhD student Andrew Antiohos and Professor Graham Thorpe from the School of Engineering and Science have taken a leaf out of the owl's book of aerodynamic wisdom. They have investigated the wakes shed by air flowing over long square cylinders and over similar cylinders that have wavy leading edges. The research is expected to result in more efficient designs of building structures, air conditioning components and aircraft.
"One reason that owls fly silently is that they have comb-like feathers on the leading edges of their wings, and these gently disturb the flow of air over the wing surfaces, preventing the air from flowing in a violent and noisy disorganised way," Mr Antiohos said.
"The combs also help owls maintain stable flight when lining up their prey. Owls deploy other cunning methods to reduce their noise levels and air resistance – some of their feathers are soft and act as good sound absorbers, and the feathers along the trailing edges of their wings have evolved to reduce resistance forces."
Inspired by the owl's example, researchers have investigated the wakes shed by air flowing over long square cylinders and over similar cylinders that have wavy leading edges. Results show remarkable differences in the air flows, with a 30% reduction in air resistance in the wavy cylinder compared to the plain flat one.
Mr Antiohos and Professor Thorpe have recently been joined by two more PhD students, Igor Grossman and Mahmud Rahman. Mr Grossman is studying how the wavy leading edge affects sound generation by the wake and Mr Rahman is studying how the different geometries impact on the mixing of fluids downstream of the cylinders.