Phys.org September 17, 2021
To measure turbulent flows the movement of tracers that are added to the fluid are tracked. The tracers spread over time, they move far apart, and every particle moves independently. To overcome these issues an international team of researchers (Switzerland, Italy, Sweden) used fibers instead of tracer particles. They created a computer simulation and added rigid fibers of different lengths, which kept the ends of each fiber apart at a fixed distance. By tracking how each fiber moved and rotated within the fluid over time, the researchers were able to build up a picture that encompassed the full scale and structure of the turbulent flow. They were able to measure the difference in the speed and the direction of the flow at two points a fixed distance apart, see how these differences change depending on the scale of the eddy and accurately measure the rate at which the kinetic energy of the fluid was transferred from the largest to the smallest scales, where it was dissipated by heat. In laboratory experiments using fibers made from nylon and the other from polydimethylsiloxane they got similar results to the simulation. As the movement of the rigid fiber ends is restricted, they developed a theory that took these limitations of movement into account. The results obtained from the two different methods were similar, verifying that the fiber method and the newly developed theory gave accurate information. The technique can be used for studying turbulence in ocean currents and fully understanding turbulence…read more. TECHNICAL ARTICLEÂ
The swirls and eddies in turbulent flows occur at a wide range of scales. Credit: Complex Fluids and Flows Unit, OIST