Breakthrough in understanding resistance in transitional flow

Physicists claim to have found a solution to understanding transitional flow, something which could be of huge significance to the fluid handling industry.

Equations developed by British physicist Osborne Reynolds more than 130 years ago to describe fluid flowing at various speeds are still widely used today. When a fluid runs slowly its flow is smooth, but when it runs quickly its flow is more chaotic.

Reynolds described fluid flowing at low speed as laminar (it flows smoothly in a single direction), and fluid at high speed as turbulent (it experiences chaotic changes in pressure and energy). Reynolds’ equations describe the relationship between the speed at which a fluid flows and the friction that is created between it and the pipe.

Engineers in the fluid handling sector still use Reynolds’ ‘laws of resistance’ to calculate how much energy is lost to friction when a liquid or gas flows through a pipe. However, with transitional flows – when a flow switches between laminar to turbulent, the laws of resistance have hitherto remained unknown.

“In transitional flow, friction varies with no discernible patterns,” says Dr Rory Cerbus, postdoctoral researcher at the Okinawa Institute of Science and Technology University (OIST).

Understanding friction values helps engineers determine the amount of energy required to pump a liquid in a pipe. If the amount of energy required to pump fluid through a pipeline when it’s in a transitional state could be calculated, it would help a range of fluid handling industries minimise waste and boost efficiency.

Cerbus, along with colleagues at OIST’s Fluid Mechanics and the Continuum Physics Unit, worked to develop a solution to this problem.

“We have shown that, although the transitional state appears to be a menagerie of flow states, there can all be characterised by laws we already know,” says Professor Pinaki Chakraborty, leader of the Fluid Mechanics Unit.

“This simplifies a fundamental problem.”

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