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

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.

风在地球表面以及火星等其他行星上无处不在。在任何松散颗粒源存在的地方，风的流体阻力可能会夹带和携带这些颗粒的一部分，距离从几毫米到几米不等，最终在长期悬浮的情况下，超过数千公里。因此，这些颗粒物的迁移可能影响空气质量、能见度、太阳辐射的吸收和透射、气候、土壤肥力，并通过沉积影响表面地形（如沙丘）。自1989年以来，我的研究计划的核心是由NSERC发现赠款资助的，是基于边界层风洞中的风成输运的物理学研究。世界上可能只有六个风洞设施在任何给定的时间从事这样的工作，而我在特伦特环境风洞中进行的研究计划是最长的，最不间断和最好的支持之一。与目前NSERC发现补助金提案相关的长期目标是：1）继续并扩展风中粒子传输物理学基础的基础研究，2）检查气流中形成的相干涡旋结构与沉积物表面形成的地形特征之间的关系，3）模拟和观察选定的环境控制对粉尘排放的作用。虽然这些目标是单独列出的，但它们之间有很大的重叠。具体目标将包括，例如，检查温度和湿度的变化对在表面附近移动的相对较大的颗粒的传输的影响，以及灰尘的排放。虽然粒子是从冰冻的表面发射出来的，并由冬季的风携带，但地球科学家对这些过程知之甚少。我们还打算在微观尺度上研究和量化颗粒与具有不同物理性质的床表面的碰撞。这种碰撞作为一种机制，用于打破表面和释放更多的颗粒进入气流。到目前为止，科学家们一直在二维参考系中工作;也就是说，所有的粒子都被假定为沿着气流的方向运动。对于非常重的粒子，这是不正确的。拟议的实验也将考虑展向分量。目前工作的另一个不足之处是，我们认为粗糙表面上的气流、泥沙输运和底形发展之间的关系是“单行道”。我们实验室最近的一些工作，使用简单的可视化方法，清楚地表明这个概念是不正确的。我们想扩展这些研究，通过使用激光多普勒风速测量详细的变化之间的相互作用的相干结构的气流和床面的形态动力学调整。如果我们能确切地了解运输系统是如何“关闭”的，那么也许，这些知识可以用于改善缓解策略。最后，到目前为止，所有的传输模型都假设风速是稳定的-在给定的事件中不变-但显然在自然界中并非如此。我们最近开始进行实验，研究阵风的作用。我们希望扩展这些考虑如何床表面形态响应。许多分析模型假设高度理想化的条件，不能反映自然界中发生的真实的过程的复杂性。我的研究计划的使命是理解和测量更现实的基本过程，以便更好地描述它们并预测它们的影响。