Benli Liu

Numerical evaluation of the scale problem on the wind flow of a windbreak

The airflow field around wind fences with different porosities, which are important in determining the efficiency of fences as a windbreak, is typically studied via scaled wind tunnel experiments and numerical simulations. However, the scale problem in wind tunnels or numerical models is rarely researched. In this study, we perform a numerical comparison between a scaled wind-fence experimental model and an actual-sized fence via computational fluid dynamics simulations. The results show that although the general field pattern can be captured in a reduced-scale wind tunnel or numerical model, several flow characteristics near obstacles are not proportional to the size of the model and thus cannot be extrapolated directly. For example, the small vortex behind a low-porosity fence with a scale of 1:50 is approximately 4 times larger than that behind a full-scale fence.

Computational fluid dynamics evaluation of the effect of different city designs on the wind environment of a downwind natural heritage site

Disturbance in wind regime and sand erosion deposition balance may lead to burial and eventual vanishing of a site. This study conducted 3D computational fluid dynamics (CFD) simulations to evaluate the effect of a proposed city design on the wind environment of the Crescent Spring, a downwind natural heritage site located in Dunhuang, Northwestern China. Satellite terrain data from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) Digital Elevation Model (DEM) were used to construct the solid surface model. Steady-state Reynolds Averaged Navier-Stokes equations (RANS) with shear stress transport (SST) k-ω turbulence model were then applied to solve the flow field problems. Land-use changes were modeled implicitly by dividing the underlying surface into different areas and by applying corresponding aerodynamic roughness lengths. Simulations were performed by using cases with different city areas and building heights. Results show that the selected model could capture the surface roughness changes and could adjust wind profile over a large area. Wind profiles varied over the greenfield to the north and over the Gobi land to the east of the spring. Therefore, different wind speed reduction effects were observed from various city construction scenarios. The current city design would lead to about 2 m/s of wind speed reduction at the downwind city edge and about 1 m/s of wind speed reduction at the north of the spring at 35-m height. Reducing the city height in the north greenfield area could efficiently eliminate the negative effects of wind spee. By contrast, restricting the city area worked better in the eastern Gobi area compared with other parts of the study area. Wind speed reduction in areas near the spring could be limited to 0.1 m/s by combining these two abatement strategies. The CFD method could be applied to simulate the wind environment affected by other land-use changes over a large terrain.

DATING METHODS FOR CHRONOLOGICAL STUDY OF YARDANG LANDFORMS:A REVIEW AND PERSPECTIVE IN APPLICATION

The age of the Yardang landform is the important parameter for determination of erosion rate and erosion quantity.It is also the premise for deeper understanding of the formation and evolution of the Yardang landform,and the relationship between the Yardang and environment.As a type of erosional landforms,the age of the Yardang landform always remains as a puzzle to researchers,and become a bottleneck in the study.In this article,the authors made a review of the methods for dating Yardang landform.Then,we made a testing of the methods by applying some of them to date the Yardang landform in the Dunhuang Yardang National Geo-park.Our results suggested that the Yardang landform was formed in a period not later than 10kaBP and not earlier than 39 kaBP.At last,we prospect the direction of the yardang formation chronology research.