The Ebb and Flow of Fluid Dynamics

Next time it’s raining outside, take a moment to notice how raindrops splash and dance in puddles, or watch the gurgling rush of water flowing from your drainpipes. You might be surprised to learn that there’s a whole field of science dedicated to studying this type of movement called fluid mechanics, including not just water, but all liquids and gases too. Many mechanical processes, from the brakes in your car to your home heating system or the sewage pipes underground, operate under the principles of fluid mechanics.

Professor of Mechanical Engineering, Sigurdur Thoroddsen, at King Abdullah University of Science and Technology (KAUST) in Saudi Arabia, has dedicated his life’s work to furthering our understanding of this field. He’s especially interested in turbulence and uses ultra-high-speed video imaging to study the dynamics of drops, bubbles, and multiphase flows, which contain two or more phases (e.g. oil and water or air and water). A Science Magazine YouTube video about one of his team’s experiments, showing how torpedo-like air pockets around heated metal balls in water reduce drag, has garnered over two million views. This discovery could help in the development of energy-efficient ships and other marine transportation in the future.  

Much of Sigurdur’s work involves using expensive high-tech cameras and lasers, but he’s also been pioneering a new, cheaper technique using smartphones to study turbulence in 3D. Turbulence has many applications in industry, for example, it mixes up liquids in pipes and transports heat. He says, “The holy grail of turbulence research is to study the three-dimensional velocity field. So if you have four cameras, you can track particles in 3D, and that will allow you to calculate the vorticity field [related to the motion of a fluid in a vortex] in three dimensions.” Using a combination of high-powered red, green, and blue LEDs in the background and four smartphone cameras, his team were able to compensate for the lower frame rate of the smartphones compared to the higher specification cameras and track the coloured shadows of the particles as they moved.

Sigurdur was attracted to KAUST in 2009 as a founding faculty member because of its excellent support for researchers. The university ensures that researchers have the equipment they need to be successful. While KAUST is a relatively new institution, over time it has established itself as a powerhouse for research with world-class facilities. He says, “We have guaranteed baseline funding every year to hire people and buy equipment, so it was very attractive for somebody like me who needs state-of-the-art experimental instrumentation.” This funding has given him the freedom to pursue his interests and enabled him to recruit high-caliber students and postdocs to work in his lab. This, in turn, has resulted in many highly cited publications and enhanced his reputation for stellar research.

Another benefit of working at KAUST is that it encourages interdisciplinary research and also provides funding for collaborators to come from abroad. Sigurdur says, “I have one collaborator here now from UC Irvine who’s an expert in cryogenics. He’s helped me design and build a cryostat where we can cool liquid helium down to one degree Kelvin [-272.15 °C]. And what happens is that the liquid becomes superfluid, so the fluid now flows without any viscous resistance. With this optical cryostat, we can see what’s going on in the fluid.” Sigurdur and his colleagues are also compressing the liquid helium until it forms a solid. Their aim is to study some strange waves which can form at the interface between the solid and liquid forms. Using a high-speed camera, they’re looking at the breakup of the liquid into jets and varying the temperature until the liquid turns into a gas. This allows them to study a wide range of fluid dynamics phenomena in just one setup. Their work has many applications including the development of fuel injection engines, inkjet printers, or even for friendly water-gun fights.

Describing himself as an academic nomad, Sigurdur moved to KAUST after long stints in the US and Singapore. As an Icelander used to inclement weather, he enjoys the warm climate and the accompanying lifestyle. He says, “We have five very good months like in California, from November to March. It takes me about eight minutes to ride my bike from my house, which is on the beach, and I’m in my office in ten minutes. It rains once a year, maybe, so I never have to put on a raincoat.” He believes that this, along with the baseline funding and support of the university, makes KAUST a very enjoyable place to work.