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Turbulent mixing of a passive scalar: Statistics of the cliffs
| Content Provider | Semantic Scholar |
|---|---|
| Author | Moisy, Fr'ed'eric Willaime, Herv'e Andersen, Jacob Sparre Tabeling, Patrick |
| Abstract | The small scale persistence of anisotropy in turbulent mixing of a passive scalar is known to be related to the presence of cliffs [1], large-scale scalar jumps concentrated over small separations. However the link, if any, between cliffs and inertial range anomalous scaling remains far from clear. We report here a detailed study of cliff statistics, obtained from one-point temperature time series in a high-Reynolds number turbulence experiment in low temperature helium gas. We will focus on statistics of spatial organization of high temperature gradients, giving evidence of self-similar clustering for inertial range separations. The flow takes place in a cylindrical vessel, 20 cm in diameter, and is generated between two coaxial disks, 13 cm apart [2], rotating in the same direction. The fluid is helium gas at a temperature of 8 K and at pressures ranging from 0.3 to 3 bar. Thermal fluctuations, of typically 50 mK, are induced by the means of a heated grid, and temperature measurements are performed at a position 30 mesh sizes downstream. The hand-made thermometers are 7 μm diameter carbon fiber, working in constant current mode, with a resolution of 100 μK. For this first study of temperature measurements we restrict ourself to a range of microscale Reynolds numbers Rλ from 100 to 300. The turbulence parameters are determined from velocity measurements at the same point and in the same flow configuration. The integral length scales of temperature (θ) and velocity (u) fluctuations are respectively Λθ = 0.7 cm and Λu = 1.0 cm, with no noticeable Rλ dependence, and the Kolmogorov scale η lies between 185 and 39 μm. The thermal cliffs are defined from a simple threshold on the temperature derivative, |∂θ/∂x| > s 〈(∂θ/∂x)〉, |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | http://www.fast.u-psud.fr/~moisy/papers/moisy_etc8.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
