Numerical Study Of The Effect Of Boundary Layer Changes On The Large Vortex Structures

Atmospheric boundary layer is the very bottom of the troposphere, which directly influenced by the earth surface through various forms of exchange interaction and terrain factors, such as the molecular viscosity, turbulent friction, radiation heat gain, water vapor exchange and material diffusion. So far, numerous studies, in forms of theoretical research and observation experiments, have been carried out for the analysis and comprehensive understanding of atmospheric boundary layer. However, due to the complexity of the fluid motion in the boundary layer, further studies into the material and energy exchange process are still necessary.In the actual geographic conditions, with buildings in the town, rivers, forests, crops and the topographic relief, non-uniformity of the underlying surface exists. This heterogeneity has impacts on the structures of the atmospheric boundary layer, causing the surface land non-uniformity of multiple scales. Under different conditions, the exchanges of water, heat and momentum in the boundary layer consequently change, which in turn affect the free movement of atmosphere and bring about weather and climate changes.In this paper, a method of the combination of compact finite difference of variable step size, high accuracy and high-resolution with Fourier spectral expansion is employed to solute the incompressible NS equations. In this algorithm a discrete scheme, in association with theory of hydrodynamic stability, of third order accuracy mixed explicit-implicit is used to study the nonlinear evolution of large vortex structures in the boundary layer with different wall characteristics.Because of the geographic complexity and diversity, an artificial uniformity or non-uniformity velocity field may be induced on the boundary layer to numerically simulate the nonlinear evolution of large eddy structures in the boundary layer with different wall characteristics. The results show that, with the same velocity structures of the induced wall, the greater its speed intensity, the greater influence it has on the nonlinear interaction of the large eddy; with the same speed strength of the velocity structure of the induced wall, the more similar structures, the better uniformity of the terrain and the smaller influence it has on the nonlinear interaction of the vortex; with the same speed strength of the velocity structure of the induced wall, the structure of the velocity distribution makes prominent difference to the nonlinear interaction; with the different wall characteristics, in the nonlinear evolution, staggered high and low speed stripe structures increase gradually in the spanwise and streamwise direction, presenting symmetry stripe structure and the phenomena of the strong ejection and sweeping.