几种地表条件下沙粒运动特征和湍流猝发检测的风洞实验研究

发布时间：2018-05-19 18:18

本文选题：风洞实验 + 风沙跃移运动　；参考：《兰州大学》2016年博士论文

【摘要】：目前针对非平坦地形上风沙流中跃移沙粒的运动特征研究尚不完善,多数风沙输运模型和风沙流运动的研究都是基于平坦地形进行的,相关研究成果如何准确合理的应用于自然界中的复杂地形条件,仍有许多问题亟待解决。本文选用自然沙漠地形中最具代表性的新月形沙丘的二维剖面作为复杂地形的代表模型,通过研究跃移沙粒在坡面上的运动规律,为深入开展复杂地形形态下风沙流运动的数值模拟和理论分析工作提供基础;同时针对风沙运动中所关注的一些微观和宏观内容,结合已有的平坦地形条件下的沙粒运动特征结果,采用PDA(Phase Doppler Anemometer)测量近地表沙粒运动状态和PIV(Particle Image Velocimetry)测量空中沙粒运动状态的相结合的方式,对坡面地形上沙粒的速度分布,粒径分布及颗粒的湍流强度等物理量进行了风洞实验研究,给出了坡面地形下沙粒的运动规律;通过Mu-level检测函数对多种地形下近壁面湍流猝发猝发频率进行检测分析。本论文的主要研究成果如下:1.利用PDA对迎风坡和背风坡上的跃移沙粒速度进行测量,并总结了跃移沙粒在坡面上的运动规律,给出了迎风坡和背风坡上沙粒速度及其水平分量和垂向分量的概率分布分布函数,坡面上沙粒平均速度与坡面上不同位置的关系,沙粒冲击速度和起跳速度的关系;总结了沙粒冲击角和起跳角的分布规律,背风坡沙粒湍流强度沿高度的变化规律。2.利用PIV对背风坡区域内空中沙粒的运动特征进行了测量和分析,总结了空中沙粒的平均速度分别随来流风速和高度的变化规律,给出了相应的关系式;总结了空中沙粒的平均粒径分别随来流风速和高度的变化规律;针对空中沙粒的速度和粒径概率分布进行了分析,并给出了向上运动沙粒和向下运动沙粒平均速度和平均粒径与来流风速之间的关系;通过对背风坡区域内床面起沙率的结果分析,给出了床面起沙率以及起沙颗粒的平均粒径与来流风速的关系式。3.利用一维热线测速仪对四种常见地貌形态下近壁面的流场特性进行了测量、统计并分析,利用Mu-level采样函数对近壁面的湍流猝发频率进行了检测,总结了近壁面流场中流体雷诺应力和湍流强度的变化规律,并统计并比较分析了不同地貌形态下近壁面流场中的湍流猝发频率。本论文利用PDA和PIV两种测量设备相结合的方式,给出了坡面地形下从迎风坡到背风坡的沙粒运动规律及坡面不同位置对跃移沙粒运动的影响。本文中所得到的坡面上沙粒冲击和起跳初速度分布函数,沙粒的角度分布函数以及背风坡区域的床面起沙率可以直接应用于复杂地形条件的风沙运动数值模拟研究;本文中所发现的跃移沙粒运动规律可以直接用于复杂地形条件下风沙运动理论分析研究,为更好地研究复杂地形下风沙运动提供了实验数据资料。
[Abstract]:At present, the research on the movement characteristics of leaping sand particles in wind-sand flow on uneven terrain is not perfect. Most of the research on wind-sand transport model and wind-sand flow movement are based on flat terrain. There are still many problems to be solved how to apply the related research results to the complex terrain conditions in nature. In this paper, the two dimensional section of the crescent dune, which is the most representative of the natural desert terrain, is chosen as the representative model of complex terrain. It provides the foundation for further numerical simulation and theoretical analysis of wind-sand flow under complex topography, and also aims at some microscopic and macroscopic contents concerned in wind-sand movement. Combined with the results of sand movement in flat terrain, the velocity distribution of sand particles on slope terrain is measured by using PDA(Phase Doppler method and PIV(Particle Image velocimetric method. The particle size distribution and turbulence intensity of particles were studied by wind tunnel experiments, and the motion law of sand particles in slope terrain was given, and the frequency of turbulence burst near the wall was detected and analyzed by Mu-level detection function. The main research results of this thesis are as follows: 1. PDA was used to measure the velocity of leeward and leeward sand particles, and the movement of leeward sand particles on the slope was summarized. The probability distribution function of sand particle velocity and its horizontal and vertical components on upwind and leeward slopes, the relationship between average sand velocity and different positions on slope surface, and the relationship between sand impact velocity and take-off velocity are given. The distribution of impact angle and take-off angle of sand is summarized, and the variation rule of sand turbulence intensity along the height of leeward slope is discussed. The motion characteristics of sand particles in the leeward slope are measured and analyzed by PIV. The variation of the average velocity of sand particles with the incoming wind speed and height is summarized, and the corresponding relationship is given. The variation of the average particle size with the wind speed and height of the incoming flow is summarized, and the distribution of the velocity and the particle size probability of the sand particles in the air are analyzed. The relationship between the average velocity and average particle size of sand particles moving upward and downward and the wind speed of incoming flow are given, and the results of sand rise rate on bed surface in leeward slope region are analyzed. The relationship between the sand rise rate on the bed surface and the mean particle size of the sediment particles and the wind speed of the incoming flow is given. The characteristics of flow field near the wall of four common landforms were measured by one dimensional hot-wire velocimeter. The frequency of turbulence burst near the wall was detected by Mu-level sampling function. The variation of Reynolds stress and turbulence intensity in the near wall flow field is summarized, and the turbulent burst frequency in the near wall flow field under different geomorphology is analyzed and statistically analyzed. In this paper, the movement of sand particles from upwind slope to leeward slope and the influence of different positions on the movement of leeward sand particles in slope terrain are given by combining PDA and PIV. The initial velocity distribution function of sand impact and take-off on slope, the angle distribution function of sand and the sand rise rate in leeward slope can be directly applied to the numerical simulation of sand movement in complex terrain. In this paper, the movement law of leaping sand particles can be directly used in the theoretical analysis and study of wind-sand movement under complex terrain, which provides experimental data for better study of wind-sand movement under complex terrain.
【学位授予单位】：兰州大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：P931.3

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