Mechanics of Particle Entrainment and Transport by Wind

粒子夹带和风传输的力学

• 批准号: RGPIN-2014-04717
• 负责人: McKennaNeuman, Cheryl
• 金额: $ 3.13万
• 依托单位: Trent University
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2017
• 资助国家: 加拿大
• 起止时间: 2017-01-01 至 2018-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=633809
• 关键词: Mechanics; Particle; Entrainment; Transport; Wind; Mechanics; Particle; Entrainment; Transport; Wind

Wind is ubiquitous at the Earth’s surface, as well as on other planetary bodies such as Mars. Where any source of loose particles exists, the fluid drag of the wind may entrain and carry some fraction of these particles over distances varying from just a few millimeters to several meters and ultimately in the case of dust in long term suspension, over thousands of kilometres. As such, the transport of these particles may affect air quality, visibility, the absorption and transmission of solar radiation, climate, soil fertility, and through deposition, surface topography (e.g. dunes). The core of my research program funded by NSERC Discovery Grants since 1989 is based upon investigation of the geophysics of aeolian transport in a boundary layer wind tunnel. There are only perhaps a half dozen wind tunnel facilities in the world that are engaged in such work at any given time, while the research program that I have carried out in the Trent Environmental Wind Tunnel is one of the longest, most uninterrupted and best supported. The over-arching, long term goals tied to the present NSERC Discovery Grant proposal aim to 1) continue and extend fundamental investigations of the physics underlying particle transport by wind, 2) examine the relations between coherent vortex structures formed in airflows and the topographic features formed on the surface of sedimentary deposits, and 3) simulate and observe the role of selected environmental controls on dust emission. Although these goals are listed separately, there is strong overlap between them. Specific objectives will include, for example, examining the effects of changing temperature and humidity upon the transport of relatively large particles traveling near the surface, and the emission of dust. Although particles are emitted from frozen surfaces and carried by winter-time winds, geoscientists know little about these processes. We also intend to examine and quantify at a micro-scale, the collision of particles with bed surfaces having varied physical properties. Such collisions serve as a mechanism for the break-down of the surface and the release of further particles into the airflow. Up to this point in time, aeolian scientists have worked exclusively in a two-dimensional frame of reference; that is, all particles are assumed to travel in the direction of the airflow. For very heavy particles this is not true. The proposed experiments will consider the span-wise component as well. Another deficiency in current work is that we have considered the relationship between the airflow, sediment transport, and bedform development on rough surfaces to be a ‘one-way street’. Some of the recent work from our lab, using a simple visualization approach, clearly shows that this concept is incorrect. We would like to extend these studies by using laser Doppler anemometry to measure in detail the changing interaction between the coherent structures in the airflow and the morphodynamic adjustment of the bed surface. If we can understand exactly how in nature the transport system is ‘shut down’, then perhaps, this knowledge can be used in improving upon mitigation strategies. Finally, all transport models to this date assume that the wind speed is steady – invariant throughout a given event - but obviously in nature it is not. We have recently embarked on experiments which investigate the role of wind gusting. We wish to extend these to consider how the bed surface morphology responds. Many analytical models assume highly idealized conditions that do not reflect the complexity of real processes occurring in nature. The mission of my research program is to understand and measure fundamental processes that are more realistic, so that they can be better described and their impacts predicted.

风在地球表面以及其他行星体（如火星）上无处不在。如果存在任何松散的颗粒来源，风的流体阻力可能会进入，并将这些颗粒的一小部分带到距离上，从仅几毫米到几米，最终在长期悬浮液中，最终数千公里。因此，这些颗粒的运输可能会影响空气质量，可见性，太阳辐射，气候，土壤肥力的抽象和传播以及通过沉积，表面形貌（例如沙丘）。自1989年以来，由NSERC Discovery Grant资助的我的研究计划的核心是基于对边界层风洞中风化风体运输的地球物理学的投资。在任何给定时间，世界上只有六个风洞设施从事此类工作，而我在Trent环境风洞中进行的研究计划是最长，最不间断且最受支持的研究计划。与当前的NSERC发现赠款提案相关的超级目标的目标是1）继续并扩展了风向粒子运输的物理物理的基本投资，2）检查在空气流中形成的相干涡流结构与在沉积沉积物表面上形成的地形特征形成的相干涡流结构之间的关系，以及3）模拟和3）模拟和3）在所选择的Emsision of Emport of Emsision of Emsision中的作用。尽管这些目标是单独列出的，但它们之间存在很强的重叠。特定的目标将包括检查温度和湿度变化对相对较大的颗粒在地面附近传播的影响以及灰尘的发射的影响。尽管颗粒是从冷冻表面发出的，并由冬季风携带，但地球科学家对这些过程一无所知。我们还打算在微尺度上检查和量化粒子与床表面的碰撞具有不同的物理特性。这种碰撞是表面分解的机制，并释放了进一步的颗粒到气流中。到目前为止，风险科学家一直在二维参考框架中工作。也就是说，所有颗粒都被认为沿气流的方向传播。对于非常沉重的颗粒，这是不正确的。提出的实验也将考虑跨度组件。当前工作的另一个缺陷是，我们考虑了气流，沉积物运输和粗糙表面上的床形开发之间的关系，是“单向街道”。使用简单的可视化方法，我们实验室的一些最近工作清楚地表明，这个概念是不正确的。我们想通过使用激光多普勒动态学扩展这些研究，以详细测量气流中相干结构与床表面的形态学调整之间不断变化的相互作用。如果我们可以准确地了解运输系统的自然界“关闭”，那么也许可以将这些知识用于改善缓解策略。最后，到目前为止，所有运输模型都假定风速稳定 - 在给定的事件中不变 - 但显然在自然界中不是。我们最近开始研究了调查风肠作用的实验。我们希望将其扩展为考虑床表面形态的反应。许多分析模型都假设高度理想化的条件不反映自然界中真实过程的复杂性。我的研究计划的使命是了解和衡量更现实的基本过程，以便可以更好地描述它们并预测其影响。