The Times - UK (2022-01-19)

18 Wednesday January 19 2022 | the times

News

The owl is a silent beast, gliding
through the woods. The drone is rather
less silent — making an irritating
buzzing sound that quickly gets it
banned from public places.
Now scientists have suggested that
drones, as well as wind turbines and
planes, could learn something from
owls.
By designing an aerofoil with the
cross section of an owl wing and the
same structure formed by the feathers
along its trailing edge, researchers have
calculated that they can reduce the
noise of artificial wings.
The research is far from the first to
show that copying owl wings can help
to cut noise. When it goes on a hunt, the
flight of an owl can be so quiet that it
cannot be heard above the rustling of
the leaves, a fact that has long been an
inspiration to engineers.
Among several techniques, one of
the ways in which owls are so quiet
comes through using a pattern of serra-
tions to break up the disordered airflow
and turbulent vortices that form at the
trailing edge of their wing.
This technique has been copied
already, but not perfectly. By making
these trailing edge serrations asym-
metric — like on an owl — the scientists
found that the dampening effect was
even more marked.
Xiaomin Liu, from Xi’an Jiaotong

University in China, said that it was

obvious there was still a lot we could

learn from owls, and that we have only

just begun to exploit their techniques.

“As masters of silent flight, owls profit

from a leading-edge comb, trailing-

edge fringe, and downy wing surface, as

well as a unique wing cross-section.

How these characteristics correlate

How it works

Owl-based

aerofoil

Serrations on trailing edge

prevent the formation of

noisy vortices

Asymmetric-

arc

Source: Xi'an Jiaotong University

Silent owls inspire quest for

quieter drones and aircraft

with acoustic and aerodynamic per-

formance remains a mystery,” he said.

The combined effect, however, is

clear. “Nocturnal owls produce about

18 decibels less noise than other birds at

similar flight speeds due to their unique

wing configuration.”

He said that the study, which used

computer modelling to calculate that

the asymmetrically-serrated wings also

had a better lift-to-drag ratio, could

help to make wind turbines more

acceptable as well.

“The trailing-edge noise scattered by

rotating machinery is a major source of

disturbance to the public,” he wrote in

the journal Physics of Fluids.

Seeing if owl-inspired wings are

really a practical solution will require

testing them in the real world and

across different uses, he said — but it is

clear that the demand is there.

“At present, the blade design of rotat-

ing turbomachinery has gradually

matured, but the noise reduction tech-

nology is still at a bottleneck,” he said.

Liu added that even if we can master

the silent flight of an owl, the birds still

had plenty of tricks to inspire future

engineers, some of which may also

hinge on the aerodynamic calculations

they had begun.

“When the owl catches prey, the

shape of the wings is also constantly

changing, so the study of the wing edge

configuration during owl flight is of

great significance,” he said.

Tom Whipple Science Editor

T

here is one

large pot, 56

pints of beer

and eight big

straws.

Welcome to a party in

the Caucasus more

than 5,000 years ago

(David Sanderson and

Norman Hammond

write).

The oldest surviving

drinking straws have

been identified after

researchers found

traces of barley starch

within the metre-long

decorated tubes.

They also contained

metal strainers that

filtered out impurities

common in ancient

beer. Strainers were

also a feature of straws

used by Sumerian

cultures, according to

a paper published in

the Antiquity journal.

The straws were

found at the early

Bronze Age Maikop

kurgan burial site in

the western Caucasus

region of southern

Russia in the late 19th

century.

Previous research

suggested that the

objects, which are on

display at the State

Hermitage Museum in

St Petersburg, were

sceptres or poles for a

canopy.

However, the

discovery of barley

starch granules and

the parallels with

Sumerian boozing

techniques point to

their true use, the new

paper said — even if

researchers could not

confirm that the

barley had been

fermented.

Viktor Trifonov, the

lead author of the

paper, from the

Russian Academy of

Sciences in St

Petersburg, said: “The

turning point was the

discovery of the barley

starch granules [which

was] direct material

evidence of the tubes

from the Maikop

kurgan being used for

drinking.”

A large vessel

capable of holding 56

pints was also

discovered at the site.

“Before having done

this study, I would

never have believed

that in the most

famous elite burial of

the Early Bronze Age

Caucasus, the main

item would be neither

weapons nor jewellery,

but a set of precious

Share beer? That

is the first straw

Serrations on owl wings cut noise

WANG AND LIU