Few PhD students can lay claim to helping establish if there is life on Mars, but Lidia Caros Roca may be the exception that proves the rule.
Thanks to her invention of a virtual wind tunnel simulator that recreates Mars’s atmospheric conditions, the Imperial College London doctoral student has paved the way for the creation of helicopters even better optimised for Martian exploration than Nasa’s Ingenuity Mars Helicopter which successfully landed on the red planet last year.
By comparing her simulation results with those from the real-life Mars Wind Tunnel in Tohoku University, Japan, she found they recreated Mars's atmosphere with a much higher degree of accuracy than had previously been possible.
The outcome is that helicopters can now be engineered to fly longer distances at higher altitudes with heavier payloads in Martian conditions — “the equivalent of getting a dragonfly and an insect flying at the same speed as an Airbus or a Boeing”, Ms Roca told The National.
“Our simulator will help to design fundamentally new blades that will perform efficiently on Mars,” she said.
“The aim was to get the same results in simulations as in the experiments in a particular Martian wind tunnel here on Earth.
“We kept adding physics into the simulations to get the same result as in the experiments and all that is useful to prove that our simulations can simulate Martian conditions, and now they can be used for designing new blades for Mars helicopters.”
Though they are considered planetary siblings, the atmospheres of Earth and Mars are radically different, with the red planet's atmosphere about 100 times thinner than ours.
This presents scientists with unique challenges in designing helicopters that can generate enough lift to take off in “air” that is less dense and with higher wind speeds.
“The Martian atmosphere has a very low density — the air is as thin as the Earth’s atmosphere at very high altitudes,” said Ms Roca.
“Conventional blades have benefited from over 100 years of aeronautical design experience. However, the low density and low speed of sound on Mars presents a flight regime unlike anything encountered on Earth, making such blades inefficient for Martian flight.”
This unusual combination means that simple modelling strategies do not yield accurate results. Instead, Ms Roca and her Imperial team used their own, in-house high-fidelity solver called PyFR to directly simulate the governing equations of motion on Mars.
They ran the simulations on some of the world’s largest supercomputers, including EPCC’s Cirrus in Edinburgh and Piz Daint at the Swiss National Supercomputing Centre, using graphics cards initially designed for use in computer gaming to make such complex simulations possible.
Where angles fear to tread
Previous attempts to simulate the experiments at Tohoku University were less successful when the blades were mounted at a high angle-of-attack, which refers to the angle between the blade and the oncoming flow.
Ms Roca's research team gradually increased the realism of their simulations and showed that only when the full span of the blade plus the wind tunnel walls were fully simulated did the results come close to the Tohoku experiments.
Further, their simulations were able to predict a key change in the behaviour of the blade with angle-of-attack. At a particular incidence, the lift mechanism of the blade changes suddenly with the formation of a large vortex that acts to “suck” on the top surface of the blade, increasing its lift.
The next step for the researchers will be to use their simulator to test specific aerofoil shapes. Dr Roca’s colleague, Dr Oliver Buxton, told The National a deal has been struck with a certain US space exploration agency but was unable to reveal any more details.
And it may not only be aerospace companies interested in the Mars-proof rotor blades: the miniature blades can also be used for applications in Earth's more benign atmosphere. Given its need for covert surveillance, the defence industry will certainly be an interested party.
“There's lots of micro drones that are used for all sorts of things like deliveries,” said Dr Buxton. “For example, you put cameras on them to inspect systems like pylons or buildings or bridges.”
It all goes to show that good things really do come in small packages.