دانلود رایگان مقاله شبیه سازی عددی 3D روند تکاملی بادی تپه های شنی هلالی شکل کوچک

abstract

A dune constitutive model was coupled with a large eddy simulation (LES) with the Smagorinsky subgridscale (SGS) model to accurately describe the evolutionary process of dunes from the macroscopic perspective of morphological dynamics. A 3D numerical simulation of the evolution of aeolian downsized crescent-shaped dunes was then performed. The evolution of the 3D structure of Gaussian-shaped dunes was simulated under the influence of gravity modulation, which was the same with the vertical oscillation of the sand bed to adjust the threshold of sand grain liftoff in wind tunnel experiments under the same wind speed. The influence of gravity modulation intensity on the characteristic scale parameter of the dune was discussed. Results indicated that the crescent shape of the dune was reproduced with the action of gravity during regulation of the saturation of wind-sand flow at specific times. The crescent shape was not dynamically maintained as time passed, and the dunes dwindled until they reached final decomposition because of wind erosion. The height of the dunes decreased over time, and the height– time curve converged as the intensity of modulation increased linearly. The results qualitatively agreed with those obtained from wind tunnel experiments.

5. Conclusion

In this study, large eddy simulation was coupled with a dune constitutive model. This approach was used in the 3D numerical simulation for the entire aeolian flow field to investigate the evolutionary characteristics of downsized crescent-shaped dunes under the influence of gravity modulation. Results show that the proposed model can reproduce a crescent shape, which is not strictly symmetrical. The unstable evolution rule of dune from the simulation agrees with that from the corresponding wind tunnel experiments. Dune height decreased over time, and the height–time curve gradually converged with the linear increase in gravity modulation; this finding agrees approximately with the result of the wind tunnel experiment. Hence, the gravity modulation mechanism embedded in the present model potentially affects the regulation of the saturation level of sand flux above the dune surface, thereby considerably producing the macroscopic crescent-shaped dune configuration at the laboratory scale. The simulation outcome agrees with the experimental results, thereby indicating that the proposed modelling approach could facilitate the study of the morphodynamic process of aeolian dunes at the laboratory scale and their comparison with natural cases. Furthermore, this model combined with the computational fluid dynamics framework to investigate the interaction dynamics of two or more barchans in depth is feasible because it can reveal reverse flow at the lee. Finally, morphodynamic modelling of aeolian dunes (Parteli et al., 2014b) has provided insights for developing application models for determining the effect of biogenic crust or space module of fences on dune morphology. This model is a potential tool to deepen understanding of the physical processes and fundamental principles in preventing soil erosion.