Analysis of Turbulence Collapse in the Stably Stratified Surface Layer Using Direct Numerical Simulation

• Published in: Boundary-layer meteorology 2011-05, Vol.139 (2), p.241-259
• Main Authors: Flores, O., Riley, J. J.
• Format: Article
• Language: English
• Subjects: Analysis; Atmospheric boundary layer; Atmospheric Protection/Air Quality Control/Air Pollution; Atmospheric Sciences; Boundary layers; Computational fluid dynamics; Convection, turbulence, diffusion. Boundary layer structure and dynamics; Cooling; Direct numerical simulation; Earth and Environmental Science; Earth Sciences; Earth, ocean, space; Exact sciences and technology; External geophysics; Fluid flow; Grounds; Mathematical models; Meteorology; Open channel flow; Open channels; Planetary boundary layer; Simulation; Turbulence; Turbulent flow
• ISSN: 0006-8314; 1573-1472
• DOI: 10.1007/s10546-011-9588-2

The nocturnal atmospheric boundary layer (ABL) poses several challenges to standard turbulence and dispersion models, since the stable stratification imposed by the radiative cooling of the ground modifies the flow turbulence in ways that are not yet completely understood. In the present work we perform direct numerical simulation of a turbulent open channel flow with a constant (cooling) heat flux imposed at the ground. This configuration provides a very simplified model for the surface layer at night. As a result of the ground cooling, the Reynolds stresses and the turbulent fluctuations near the ground re-adjust on times of the order of L / u τ , where L is the Obukhov length scale and u τ is the friction velocity. For relatively weak cooling turbulence survives, but when turbulence collapses, a situation that is also observed in the ABL. This criterion, which can be locally measured in the field, is justified in terms of the scale separation between the largest and smallest structures of the dynamic sublayer.