Abstract
We report measurements of the spreading rate of pairs of tracer particles in an intensely turbulent laboratory water flow. We compare our measurements of this turbulent relative dispersion with the longstanding work of Richardson and Batchelor, and find excellent agreement with Batchelor's predictions. The distance neighbour function, the probability density function of the relative dispersion, is measured and compared with existing models. We also investigate the recently proposed exit time analysis of relative dispersion.
Highlights
DEUTSCHE PHYSIKALISCHE GESELLSCHAFT turbulent velocity, the Reynolds number measures the ratio of inertial and visc√ous forces
Exit time statistics have recently been proposed as a powerful alternative to the traditional analyses of turbulent relative dispersion, and it has been suggested that they should show ‘true’ inertial range scaling behaviour even at moderate Reynolds numbers [22], [29]–[31]
We have measured the spreading of pairs of passive tracer particles in an intensely turbulent water flow, and have tested several models of turbulent relative dispersion
Summary
We generated turbulence by counter-rotating two baffled discs in a closed plexiglass cylindrical chamber containing 120 litres of water, described in detail previously [5, 6]. While this flow is both anisotropic and inhomogeneous, it can be used to achieve very high Reynolds numbers in a relatively small amount of laboratory space. The size of the apparatus makes it well-suited to Lagrangian measurements; in wind tunnels or other configurations with strong mean flows, it is significantly more difficult to follow tracer particles for long periods of time [7]. We here describe the Lagrangian particle tracking algorithms we use (subsection 2.1), the optical setup and cameras (subsection 2.2), and the calibration procedure (subsection 2.3), and show some of the parameters of our experiments (subsection 2.4)
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