Eulerian and Lagrangian statistics in stably stratified turbulent channel flows

Abstract

Using direct numerical simulation, we investigate the Eulerian and Lagrangian characteristics of the near-wall turbulence under stable stratification. In the near-wall region, large-scale motions are suppressed by stable stratification, while small-scale motions are enhanced, which leads to the increase of intermittency. It is shown that the modification of the Reynolds shear stress is caused by the increased intermittency and anisotropy. Investigation of acceleration and vorticity reveals that the length scales and timescales of the near-wall coherent vortices are reduced by stratification. The role of baroclinic torque around the near-wall turbulent structures is also discussed. The Lagrangian statistics indicate that the scaled dispersion in the streamwise direction remains unchanged, while those in the spanwise as well as in the wall-normal direction are suppressed by stratification.

Keywords:

• stable stratification
• turbulent channel flow
• Lagrangian statistics
• direct numerical simulation

Acknowledgments

The authors gratefully acknowledge the supports provided by the Yonam Foundation and the Korea Science and Engineering Foundation through grant no. R01-2008-000-10664-0 and WCU Project. The authors are grateful to Dr. J. Lim for helpful discussions. Most computations were carried out in the KISTI Supercomputing Center in Korea, and their support is also gratefully acknowledged.