Professor Dame Ann Dowling

Interview with Professor Dame Ann Dowling

As the IET gets set to host the Global Grand Challenges Summit next month, Professor Dame Ann Dowling, who is chairing the steering committee, talks about the challenges in her life - engineering, scientific, educational and human.

"I don't really believe in characterising people," replies Professor Dame Ann Dowling to the question of being a female engineer. "I just try to be a good engineer." She's not sure about the 'top engineer' label either. "My goodness," she laughs, "a top; perhaps among the top."

Dowling's engineering commitments include heading the largest engineering department in the country at Cambridge University; doing research for Rolls-Royce; being a non-executive director of BP (on their main board as well as on their Safety, Environment and Ethics Advisory Committee) and advising the government.

One example of the latter was a well-received paper on the pros and cons of nanotechnology. She chaired a Royal Society/Royal Academy of Engineering working group of engineers and scientists, which she describes as "interesting". Lord Sainsbury, who commissioned it, said it was "an example of the way in which a review of emerging technology should be done".

Global Grand Challenges

Dowling is currently chairing the steering committee for the Global Grand Challenges Summit, to be held at the IET this March. Whilst aeronautics, turbulent combustion, acoustics and vibration are her areas of expertise, grand challenges facing the globe are also close to her heart.

Four years ago, she started the Energy Efficient Cities initiative. When I ask her about Britain's wind resources and how these will feature in our low-carbon future, a large part of the solution she offers is mundane: switching things off. Dowling's department has reduced its electricity by 17 per cent by doing things like changing the cooling systems in the server rooms.

Insulation is another key element in energy use reduction, but this is tricky in old housing stock. New buildings with better insulation and upgraded transport are key. Dowling thinks that 20 per cent renewable energy by 2020 is a "very ambitious aim". Renewables will "only ever play a part in a balanced energy portfolio" and only then if better local energy storage possibilities are available. She thinks nuclear energy "has a role to play in a low-carbon future". But it's most important to control energy demand.

Dowling has had some experience of working with global challenges. Those outlined by the summit are:

1) Sustainability. What does this envisage? "Meeting modern needs without compromising the future" – i.e. looking after the world's natural resources.

2) Global health threats. Dowling doesn't like the word 'threats'. The summit will not just address challenges, she says, but also how "engineering technology can contribute solutions to those challenges". Dowling gives a specific example: the globe's ageing population. The challenge is to keep them functional. Engineers are already designing products for people with arthritis and poor eyesight. The Cambridge team has designed a large-print, easy-use phone.

3) Resilience. A broad concept, but Dowling highlights cyber-security as one aspect of virtual infrastructure. Financial resilience and the ability to handle risk is another. Smart technology is being developed to monitor physical infrastructure such as ageing bridges. New buildings could include sensors to monitor performance and ongoing modification.

What does she hope will be achieved from this summit? How likely is it that the UK, US and China will agree something concrete? It turns out this is not the main point. "It's geared at young people," explains Dowling. The idea is that the speakers will enthuse research students and graduates in their first jobs, who will spread the word.

Submarine sonar, silent aircraft and turbine targets

Dowling's specific areas of research are connected to the globe's future challenges: combustion, acoustics and vibration, leading to low-emission combustion and quieter vehicles.

After studying mathematics at undergraduate level, and following a summer job at the Royal Aircraft Establishment, Farnborough, Dowling's PhD was in aeroacoustics – 'Acoustic Sources in Motion'. Her mission was to understand the Concorde noise problem. The result was the discovery that high-speed motion affects sound generation differently to what was previously thought – it is more complicated than just Doppler factors.

After her PhD, Dowling worked on underwater acoustics, unsteady flow and combustion: "How flexible coatings over sonar could reduce the noise of turbulent flow over submarines." The oil industry is one interested party. Acoustic reflected signals can be used to detect oil-bearing rocks, she says. But unsteady flow over the towed detectors can conceal these weak signals, so Dowling was trying to get maximum signal-to-noise ratio by reducing the noise of turbulent flow over the transducers. A combination of visco-elastic materials proved to be the solution.

And so to the Silent Aircraft Initiative, an MIT/Cambridge collaboration, which Dowling led. The brief was to make passenger jet noise imperceptible outside the airfield. Its targets have inspired Nasa in its long-term research. "They've gone further," Dowling says. In Nasa's aeronautics research project "aircraft need to meet stringent low-fuel burn and noise targets".

However, the resulting SAX40 is still just a concept. For a start, there's the cost: over £20bn, Dowling estimates. The prototype used the advantages of the blended-wing body, but "ours had some novelty - an indentation under the centre body which gave a higher ratio of lift to drag than Boeing's". The style of engine was also different. Dowling explains that historically engine efficiency has been improved by having a bypass engine: "Not all the air goes through the combustion chamber; instead a turbine is used to drive a big fan, which moves a lot of air at low speed. This reduces the jet noise." But if you make the fan bigger you increase the surface area of the pods holding the engines and this increases drag, so fuel efficiency improvements peter out. The solution was to have the turbine drive three smaller fans. These could be packed into the aircraft avoiding the extra drag and reducing the weight of the engine, thereby emitting less noise and using less energy.

And why did Dowling's team employ variable area nozzles, not currently used in civil aircraft? "For low noise at take-off you need lots of low-speed airflow through the exit nozzle – the three fans could give that but for peak efficiency in cruise you want to reduce the bypass ratio," Dowling says. This is achieved by closing the exit nozzle a little. The nozzle opening can also be changed to keep the engines operating at peak efficiency as the aircraft gets lighter due to fuel consumption during flight.

Whilst current aircraft have this trade-off of reducing noise, which can increase weight and drag and bring down efficiency, their design decreased fuel burn by 20 per cent and noise by a substantial 25dB. This is defined as background noise, undetectable in ambient daytime urban conditions. Even more fuel could be saved, she says, if the noise was only reduced by 10dB.

Another application of her research is gas-fuelled power stations. Targets to reduce harmful gases like nitrous oxides are causing power stations to operate on the verge of instability. Low emission targets can be achieved by burning lean with a high ratio of air to fuel, but then the combustion is very susceptible to instability. "The large pressure oscillations can be so intense that they break the gas turbines in the power stations."

Historically, unstable combustion has happened in energy-intensive combustors like rockets and afterburners of jet engines. Dowling and her team are on the case. "We have worked on models predicting when those instabilities would happen and how they can be avoided. This can be through the way you mix the fuel and air or by increasing absorption of acoustic energy. We have also used feedback control to achieve stability. This is when you drive the fuel unsteadily to produce fluctuations in the combustion rate in anti-phase with those occurring naturally." By demonstrating on a simple combustor in the lab and then working with Rolls-Royce on a jet engine they got "active control of the instability" and eliminated the oscillations.

Engineer Deficit

Despite the enormity and importance of these projects, the shortfall in British engineers is huge. Dowling often gives talks in schools, but the message is still not getting across. In particular, it's not getting across to her own sex.

The feedstock of girls reading engineering at university is around 17 per cent, Dowling thinks. Why? The perceived lack of social relevance and flexible working hours perhaps? "Nothing could be further from the truth," protests Dowling. "Every engineering project is about making something that someone wants. It is very creative."

However, Dowling says her department has a higher percentage of female engineers than elsewhere. Could this have something to do with herself as figurehead? "I don't think I can claim that." Instead, she puts it down to offering a broad strand of engineering. However, later on she concedes that it's always useful to see someone active in your field and doing well. 

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