Engineering news
A group at the Institute of Science and Technology Austria has found a way of destabilising turbulence within a pipeline and converting it into a persistent, non-turbulent ‘laminar flow’.
The work could have huge implications across the water and oil and gas industries – pumping these fluids accounts for around 10% of the world’s electricity consumption. Much of that energy loss is caused by turbulence, which increases frictional drag.
In the past, researchers have tried to reduce turbulence at local levels. The Austrian group, led by Bjorn Hof, took a different approach. They looked at the velocity profile of a pipe in cross-section: the flow is fastest in the middle of the pipe, and slower near the walls.
Their intervention tried to reduce this difference in speed, by placing rotors in the flow to create a “flatter” profile – evening out the flow. The scientists found that this interrupted the process that created turbulent eddies, and that the fluid gradually returned to a smooth, laminar flow, and remained that way until it reached the end of the pipe.
“Nobody knew that it was possible to get rid of turbulence in practice,” said Jakob Kuhnen, a co-author of the study. “We have now proven that it can be done. This opens up new possibilities to develop applications for pipelines.”
The next step for this proof of concept is to scale up the technology so that it can work in larger pipelines and at higher speeds. But the researchers say their early investigations are promising. “In computer simulations, we have tested the impact of the flat velocity profile for Reynolds numbers [a measure of turbulence in a fluid] up to 100,000, and it has worked absolutely everywhere. The next step is now to make it work also for high speeds in the experiments,” said Hof.
A spokesperson for the Institution of Mechanical Engineers told Professional Engineering that the concept could be "hugely advantageous," in terms of energy savings. "However," they added, "there are a number of concerns which would need to be addressed, including how secure the rotors are and the risk that they could become detached thereby becoming projectiles within the pipe, the effect on average fluid velocity and the extent to which there might be a pressure drop associated with the rotors."
They also pointed out that removing turbulence with just one set of rotors may not be possible. "Practical piping systems will have a significant number of discontinuities owing to valves, instrumentation, piping junctions, pipe taps for vents and drains and meters – all of which generate turbulence. Presumably each would require a rotor device to restore laminar flow downstream the discontinuity."