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Scientists confirmed 70-year-old theory of turbulence in fluids

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Posted June 28, 2019

If you travel a lot, you know what a turbulence is. In fluid mechanics, turbulence is chaotic changes in fluid pressure and flow velocity. In aviation, turbulence causes an uncomfortable ride, but in shipping and various pipes turbulence characterises losses of energy. But what is it really? Scientists from the University of Queensland and Monash University managed to verify a 70-year-old theory of turbulence in fluids.

70 year ago Nobel Laureate Lars Onsager created a theory that vortices form when enough energy is added to a two-dimensional system. Now scientists can confirm that. Image credit: Yuri Filippov via Wikimedia (CC BY 4.0)

Transporting fluids over pipes requires a tremendous amount of energy. Huge losses are due to friction and turbulence. For the longest time scientists haven’t been able to explain the phenomenon. However, 70 years ago there was a promising theory, which was never fully confirmed. It was created by the Nobel Laureate Lars Onsager and it stated that if you add enough energy to a two-dimensional system, turbulence will cause giant vortices. Now, vortices are pretty much a guarantee of turbulence, but the theory hasn’t been verified for all those years.

Scientists created a superfluid by cooling a gas of rubidium atoms almost to absolute zero. Then they needed a way to create vortices. Researchers chose lasers – they aimed lasers very precisely, essentially stirring the liquid in the same way you stir your tea. And it worked. The added energy to this two-dimensional fluid created vortices (a situation where flow revolves around an axis line), essentially confirming the old Onsager’s theory on turbulence. Scientists were surprised to see the vortices forming just as a result of shining laser. Dr Tyler Neely, one of the authors of the study, said: “It amazes me that we can do this with light and at such a small scale – the cores of the tiny vortices we created were about one tenth of the size a human blood cell”.

Of course, this is just a small step towards a better understanding of turbulence. However, it is a very important one. Scientists reminds us that turbulence causes enormous inefficiency for moving vehicles such as ships. It also makes for huge energy losses in transporting all sorts of fluids through pipes all over the world. It may be water, but it may also be something more valuable, such as fuel or oil. Those energy losses are huge and cost companies and consumers unbelievable amounts of money. A better understanding of turbulence could lead to better designs of ships and pipework.

Pipes are usually very smooth on the inside. This allows reducing friction losses. However, turbulence happens anyway. Understanding this phenomenon is key in preventing the losses.

 

Source: University of Queensland 

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