Study finds way to measure transitional flow

Researchers from Okinawa Institute of Science and Technology (OIST) have developed a method to work out friction and energy loss in a liquid when it is neither laminar nor turbulent. The finding could help fluid handling facilities improve their operations.

Analysing liquids in a transitional state has typically been impossible, as the friction varies with no observable patterns. This made it impossible to develop laws of resistance for transitional flow.

The scientists at OIST solved this problem by segmenting different sections of the flow and then studying them. They gathered data on transitional flow by adding particles to water, running it through 20m glass pipe and illuminating it with a laser. Friction caused by the liquid was measured by pressure sensors. This allowed them to identify the separate patches of laminar and turbulent flow and study them.

“We have shown that, although the transitional state appears to be a menagerie of flow states, these can all be characterized by laws we already know,” says Professor Pinaki Chakraborty, leader of OIST’s Fluid Mechanics Unit. “This simplifies a fundamental problem.”

The discovery allows for the evaluation of transitional flows using the pre-existing Reynolds number, which is used to forecast flow patterns.

A better understanding of liquid in a transitional state will allow operators of fluid handling facilities better optimise their processes and equipment.

The study, called ‘Laws of Resistance in Transitional Pipe Flows’ was published in Physical Review Letters 31 December.