Simulation of turbulence mixing in the atmosphere boundary layer and analysis of fractal dimension

Abstract

In the first part of this paper, a flow model for numerical simulation of turbulent parameters in atmospheric boundary layer (ABL), based on finite volume method and large-eddy simulation is introduced. This model consists of balance equations for mass, momentum and energy (for potential temperature) equations. The Lagrangian dynamic model of Smagorinsky with restriction of size for the coefficient Cs was used for sub grid turbulent viscosity. The second part of this paper is devoted to the numerical aspects of flow model using proper orthogonal decomposition (POD) method. In the final part of this paper, results from numerical studies on flow in ABL for the neutral and stable case and analysis of fractal dimensions are presented. These results constitute important tests for the assessment of the predictive capacity for the stratified flow model in hand. ImaCalc program was used to study the fractal parameter and structure functions. We calculated the maximum value of fractal dimension D selected among all of the velocity intensity and vorticity modules which was a good indicator of flow’s complexity. The data of evolution of D(t) in the middle section of the domain of the multifractal spectra along the main downstream axis were also calculated. The reduction in the maximum value of the fractal dimension for intermediate velocity and vorticity values is consistent with laboratory experiments and with wind wane measurements.