Kelken Chang

On integral length scales in anisotropic turbulence

We found experimentally a dependence of the integral length scales of correlation functions measured in different directions in a turbulent flow on the velocity fluctuation anisotropy in those same directions. We derive invariants for anisotropic turbulence that is locally isotropic, and so a relationship between the velocity and length scales. The results emphasize the importance of defining the Reynolds number, which was about 480, in terms of scalar quantities instead of these scales. We also find that the normalized energy dissipation rate was approximately independent of the anisotropy.

Lagrangian particle tracking in high Reynolds number turbulence

We describe a Lagrangian particle tracking technique that can be applied to high Reynolds number turbulent flows. This technique produces three-dimensional Lagrangian trajectories of multiple particles, from which both Lagrangian and Eulerian statistics can be obtained. We illustrate the application of this technique with measurements performed in a von Ka rman swirling flow generated in a vertical cylindrical tank between two counter-rotating baffled disks. The Taylor microscale Reynolds number investigated runs from 200 to 815. The Kolmogorov time scale of the flow was resolved and both the turbulent velocity and acceleration were obtained and their probability density functions measured. Measurements of the Eulerian and Lagrangian velocity structure functions are presented. The average energy dissipation rates are determined from the Eulerian velocity structure functions.