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Generating sinuous-crested bedforms from direct numerical simulations

Virtual experiments, also known as numerical simulations, are becoming a popular tool for studying geophysical problems, specifically the formation of sediment patterns such as sand ripples below unidirectional water flow. To decrease computational cost, many numerical simulations use simplifying assumptions that may lead to some modelling errors. Direct numerical simulations (DNS) are one example of numerical simulations that use very little simplifying assumptions, and are thus computationally expensive. Nonetheless, DNS are becoming increasingly popular with the rise of computational power. While DNS have proven very useful in extracting data that is otherwise very difficult to obtain experimentally, they have not been able to capture certain aspects observed in laboratory experiments. As ripples migrate downstream below the water flow, their crestlines in many cases become sinuous. This sinuosity has not been reproduced to date using DNS. A common aspect of these DNS simulations is the use of virtual flumes with no laterally bounding sidewalls. In this paper, we show that by adding virtual sidewalls to the DNS, the crestline sinuosity of ripples significantly increases. Additionally, we find that when wider virtual flumes with bounding sidewalls are used, the sinuosity is further amplified.

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