An experimental investigation of the relative diffusion of particle pairs in three-dimensional turbulent flow

Abstract

The particle tracking (PT) technique is used to study turbulent diffusion of particle pairs in a three-dimensional turbulent flow generated by two oscillating grids. The experimental data show a range where the Richardson–Obukhov law 〈r2〉 = Cεt3 is satisfied, and the Richardson–Obukhov constant is found to be C = 0.5. A number of models predict much larger values. Furthermore, the distance–neighbour function is studied in detail in order to determine its general shape. The results are compared with the predictions of three models: Richardson (1926), Batchelor (1952) and Kraichnan (1966a). These three models predict different behaviours of the distance–neighbour function, and of the three, only Richardson's model is found to be consistent with the measurements. We have corrected a minor error in Kraichnan's (1996a) Lagrangian history direct interaction calculations with the result that we had to increase his theoretical value from C = 2.42 to C = 5.5.

Table-top rotating turbulence: an experimental insight through particle tracking

“…When the separation distance exceeds the largest scales of the flow, its growth proceeds with a final asymptotic τ -regime. Recent high-Re turbulence data from experiments and direct numerical simulations (Boffetta and Celani, 2000, Ott and Mann, 2000, Mazzitelli and Lohse, 2004, between the others) confirm the Richardson τ 3 -law. It is worth to mention that other experimental data (Bourgoin et al, 2006) are instead in favour of the τ 2 -regime predicted by Batchelor (1950) in the inertial range.…”

Richardson's Law in Large-Eddy Simulations of Boundary-Layer Flows

“…On the other hand, a value C 2 ∼ O(1) (and even larger) follows from closure predictions (Monin and Yaglom, 1975). More recently, both an experimental investigation (Ott and Mann, 2000) and accurate three-dimensional direct numerical simulations (DNS) (Boffetta and Sokolov, 2002) give a strong support for the value…”

“…For a comparison see Figs. 3 and 4. The velocity field necessary to integrate (14) has been obtained by a bilinear interpolation from the eight nearest grid points on which the velocity field produced by the LES is defined.…”

Intermittent turbulence and copepod dynamics: Increase in encounter rates through preferential concentration

“…We consider here the experimental data presented in Mann et al (1999) and Ott and Mann (2000). A water tank of inner dimension 320 × 320 × 450 mm 3 , with two oscillating grids at the top and the bottom, was used to generate a flow with no mean velocity and approximately homogeneous and isotropic turbulence at the central region.…”

“…While Ott and Mann (2000) and Mann et al (2005) have considered dispersion properties using these particles, we focus here on the preferential concentration effect. Since the particle and flow characteristics are close to those corresponding to the copepod framework: the value of β is close to 1, and the Stokes number is close to the range (0.4, 1) corresponding to the preferential concentration effect, according to the numerical results reported above.…”