Formation Mechanism of Wind Ripples

几乎在所有已知的环境中，沙表面都会形成波纹和沙丘。由于它们的普遍性，地质记录中保存的涟漪对于解释过去或遥远的气候，大气条件和河流状况是非常宝贵的。在这种情况下，了解涟漪如何形成对于将其大小与环境因素联系起来至关重要。根据传统观点，地球上十米级的沙丘和分米级的涟漪是由与风运动和沙子输送有关的明显不同的过程产生的。然而，最近的实验打破了这种清晰的区别，显示出一种无法解释的第二种风涟漪的出现，在某种程度上类似于火星上的水波纹和大波纹。对这种潜在的普遍存在的新型底形的拟议调查可以改变对实地和地质记录中涟漪的解释，并揭示一些未探索的沉积物输运的复杂性。更广泛的影响包括与TAMU的外联专家合作，为K-12学生和教育工作者开发了几个公共展览。该项目还将为两位早期职业生涯的主要研究人员以及本科生和研究生提供研究和教育机会。这项研究将使用计算流体动力学（CFD）和颗粒尺度传输模拟相结合的方法来研究这些新的“流体动力学”（也称为“阻力”）涟漪在地球上的出现。目标是揭示控制地球上以及水和其他行星体（如火星、泰坦和金星）上中尺度底形（涟漪）的起源和尺度的物理机制。这三个目标是：验证和校准Hanratty的流体动力学模型，估计运输饱和长度，并解释从“影响”到“流体动力学”涟漪的过渡。中心假设是，有一个隐藏的亚尺度调制的风成输送层，可以解释新的观测和流体动力驱动的不稳定性变得不太相关，在一个足够大的粒度，只有“影响”这一奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查进行评估，被认为值得支持的搜索.

Sand surfaces develop ripples and dunes in almost every known environment. Because of their ubiquity, ripples preserved in the geological record are invaluable to interpret past or remote climates, atmospheric conditions and fluvial regimes. In this context, understanding how ripples form is crucial to relate their size to environmental factors. According to conventional wisdom, decameter-scale dunes and decimeter-scale ripples on Earth emerge from clearly different processes related to wind motion and sand transport. However, recent experiments shattered this clean distinction by showing the emergence of an unexplained second type of wind ripple, somehow akin to water ripples and large ripples on Mars. The proposed investigation of this potentially ubiquitous new type of bedform can alter the interpretation of ripples in the field and the geological record, and shed light into some unexplored complexities of sediment transport. Broader impacts include the development of several public exhibits intended for K-12 students and educators, in collaboration with outreach experts at TAMU. The project will also provide research and educational opportunities for two early career principal investigators and undergraduate and graduate students.This research will investigate the emergence of these new “hydrodynamic” (also called “drag”) ripples on Earth using a combination of Computational Fluid Dynamics (CFD) and grain-scale transport simulations. The goal is to uncover the physical mechanisms controlling the origin and scaling of meso-scale bedforms (ripples) on Earth, and by extension, on water and other planetary bodies such as Mars, Titan and Venus. The three objectives are: validate and calibrate Hanratty’s hydrodynamic model, estimate the transport saturation length, and explain the transition from “impact” to “hydrodynamic” ripples. The central hypotheses are that there is a hidden sub-scale modulation of the aeolian transport layer that can explain the new observations and that hydrodynamic-driven instabilities become less relevant at a large enough grain size, for which only “impact” ripples are to be expected.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.