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: 2014
• 资助国家: 加拿大
• 起止时间: 2014-01-01 至 2015-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=566700
• 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，只要存在任何松散颗粒源，风的流体阻力就可能夹带并携带这些颗粒的一部分，移动距离从几毫米不等。达数米，最终在长期悬浮的灰尘情况下，达数千公里。因此，这些颗粒的传输可能会影响空气质量、能见度、太阳辐射的吸收和传输、气候、土壤肥力以及通过。沉积、表面自 1989 年以来，我的研究项目一直由 NSERC 发现资助资助，其核心是基于对边界层风洞中风传输的地球物理学的研究。世界上大约只有六座风洞设施。在任何特定时间都从事此类工作，而我在特伦特环境风洞中进行的研究计划是最长、最不间断和得到最好支持的总体长期目标之一。与目前的 NSERC 发现拨款提案相关的目标是 1) 继续并扩展对风引起的粒子传输的物理基础研究，2) 检查气流中形成的相干涡流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，尽管这些目标是单独列出的，但它们之间存在很强的重叠，例如，检查温度和湿度变化对运输的影响。相对较大的颗粒在附近移动尽管颗粒是从冰冻表面散发出来并由冬季风携带的，但我们还打算在微观尺度上检查和量化颗粒与床表面的碰撞。具有不同的物理特性，这种碰撞是表面破裂并将更多颗粒释放到气流中的机制，到目前为止，风科学家一直在二维参考系中进行研究。也就是说，假设所有粒子都在运动对于非常重的颗粒，这也是不正确的，当前工作中的另一个缺陷是我们考虑了气流、沉积物传输和床形之间的关系。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，我们希望通过使用激光多普勒风速测量来扩展这些研究。详细测量相干结构之间不断变化的相互作用如果我们能够准确地理解传输系统本质上是如何“关闭”的，那么也许这些知识可以用于改进迄今为止的所有传输模型。假设风速是稳定的——在给定的事件中是不变的——但显然在自然界中情况并非如此。我们最近开始进行实验来研究阵风的作用，我们希望将这些实验扩展到考虑床表面形态的响应。许多分析模型都假设高度理想化我的研究项目的任务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。