Analysis: The flow of fluids and the transfer of heat and mass can be difficult to understand and predict but modern advances have helped bridge the gap
One thing's for sure – nature does not like to sit still. The motion of fluids like water and air has fascinated people for thousands of years. Archimedes' principle of buoyancy is an early example of this, and the remains of ancient Roman aqueducts show a sophisticated understanding of fluid mechanics that helped support ancient towns and cities.
We have always tried to understand how nature works to improve our quality of life. However, the flow of fluids and the transfer of heat and mass from one place to another can be notoriously difficult to understand and predict. Blood flow in the human body is a good example of these phenomena all working together at once. So, what can we do to start getting a grip on all this complexity?
To start, mathematics has proved indispensable in helping us to understand the natural world and predict how natural systems behave. The problem is that the equations involved can be difficult or even impossible to solve exactly. Experiments have been and remain invaluable, but sometimes measuring something can interfere with the very thing we are trying to observe.
From YouTube Channel TED-Ed, how taking a bath led to Archimedes' principle - Mark Salata
Throughout history, humans have developed tools to help them solve difficult problems and move forward. The invention of the computer fast-tracked breakthroughs in vital areas like health and energy by allowing us to tackle problems that were previously out of reach. But how can a computer be used to understand nature?
Computers have become part of our everyday lives. Now, if the right set of equations is translated into instructions that a computer can understand, something magical happens – we can mirror aspects of nature through what we call "simulation". When we use computers to simulate the movement of fluids, often alongside heat and substances carried by those fluids, we call it computational fluid dynamics. Of course, we must be careful and make sure that what we are looking at on the computer screen is right.
Artificial intelligence, or AI, is also becoming increasingly important for analysing flow phenomena, helping researchers interpret simulation data and develop faster ways of predicting how fluids will behave. Recently, OpenAI announced a proposed solution to one of the famous Millennium Prize Problems involving the Navier–Stokes equations, a set of equations used to describe how fluids move.
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The problem had remained unsolved for about 90 years and simply asked: if a fluid starts off flowing smoothly, will it also remain that way mathematically, or will something eventually go wrong? The proposed answer is that something can indeed go wrong: mathematically, the speed of the fluid can grow without limit – something that could not actually happen in a real fluid. There is something fitting about this development. We began by using computers to solve equations that were too difficult to solve by hand. Now, AI running on computers is beginning to help us investigate the equations themselves.
All of this has given us a wonderful way to look at phenomena that normally would be invisible to us, often using colourful images that can show us things like how fast a fluid is moving and where it is going. We can look at how water moves through tanks metres across to make them safer and more efficient.
We can zoom down thousands of times to watch blood cells deform as they squeeze through microscopic vessels - a little like boba balls moving through your bubble tea – and zoom in again to see how oxygen moves from a red blood cell into the surrounding tissue, all to help us design better medical technologies. This video shows a simulation of red blood cells moving and deforming inside a capillary in the eye, and if you want to know more, our paper on red blood cell sedimentation is free to read.
From YouTube channel BSC CNS, simulation of red blood cells in a retina capillary
We can also look inside a battery and watch how heat moves as it charges and discharges, like watching a heatwave appear on a weather map. Keeping that heat under control is vital: if a battery gets too hot, a phenomenon called thermal runaway can cause it to fail and even explode.
With batteries now powering everything from our phones to electric vehicles and storing energy from the sun and wind, finding better ways to keep them cool is increasingly important. At the CFD Research Group in TU Dublin supported by Enterprise Ireland, we are working with acoustic and thermal insulation engineering company Ventac to improve battery temperature control using fluid simulation. The aim is to make electric vehicle batteries safer and to increase vehicle range.
If you'd like to further explore the world of fluid simulation, Valentin Caries' Web-LBM and the University of Alberta's Eulerian Flow Tunnel let you simulate fluid flow directly in your browser. We have come a long way from Archimedes to AI – who knows what comes next?
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The views expressed here are those of the author and do not represent or reflect the views of RTÉ
