Dario Vincenzi

Acceleration Correlations and Pressure Structure Functions in High-Reynolds Number Turbulence

We present measurements of fluid particle accelerations in turbulent water flow between counterrotating disks using three-dimensional Lagrangian particle tracking. By simultaneously following multiple particles with sub-Kolmogorov-time-scale temporal resolution, we measured the spatial correlation of fluid particle acceleration at Taylor microscale Reynolds numbers between 200 and 690. We also obtained indirect, nonintrusive measurements of the Eulerian pressure structure functions by integrating the acceleration correlations. Our measurements are in good agreement with the theoretical predictions of the acceleration correlations and the pressure structure function in isotropic high-Reynolds number turbulence by Obukhov and Yaglom in 1951 [Prikl. Mat. Mekh. 15, 3 (1951)]. The measured pressure structure functions display K41 scaling in the inertial range.

Shear effects on passive scalar spectra

The effects of a large-scale shear on the energy spectrum of a passively advected scalar field are investigated. The shear is superimposed on a turbulent isotropic flow, yielding an Obukhov–Corrsin

The Kraichnan–Kazantsev Dynamo

k^{-5/3}

Vorticity moments in four numerical simulations of the 3D Navier–Stokes equations

scalar spectrum at small scales. Shear effects appear at large scales, where a different, anisotropic behaviour is observed. The scalar spectrum is shown to behave as

Nonlinear elastic polymers in random flow

k^{-4/3}

Orientation of non-spherical particles in an axisymmetric random flow

for a shear fixed in intensity and direction. For other types of shear characteristics, the slope is generally intermediate between the

Dynamical slowdown of polymers in laminar and random flows

-5/3

Regimes of nonlinear depletion and regularity in the 3D Navier-Stokes equations

Obukhov–Corrsin and the

Single polymer dynamics in elongational flow and the confluent Heun equation

-1

An overview of the statistical properties of two-dimensional turbulence in fluids with particles, conducting fluids, fluids with polymer additives, binary-fluid mixtures, and superfluids

Batchelor values. The physical mechanisms at the origin of this behaviour are illustrated in terms of the motion of Lagrangian particles. They provide an explanation for the scalar spectra that are shallow and dependent on the experimental conditions in shear flows at moderate Reynolds numbers.