U形渠道断面流速分布规律及水力特性试验研究

发布时间：2018-03-21 15:26

本文选题：U形渠道　切入点：流速分布　出处：《西北农林科技大学》2014年硕士论文　论文类型：学位论文

【摘要】：河流、渠道、以及水工隧洞中具有自由表面的水流均称为明渠水流，明渠均匀流是明渠水力计算中最基础的问题。灌溉渠系中U形渠道以其过流能力大、防渗效果好、输沙能力强、抗外力性能优越、占地面积小等优点，被广泛应用于实际生产中。鉴于其广泛应用时间较短、过水断面形状的特殊性、水流条件的复杂性等原因，U形渠道水力特性方面的研究不尽完善。本文针对U形渠道在均匀流条件下进行试验研究，以三种不同几何尺寸U形渠道作为研究对象，以流量、水深、底坡等水力因素为变量，对不同水流条件下渠道流速进行测试，分析了渠道断面流速分布，水流紊动特性，探究渠道流量计算的方法。通过研究得到以下主要结论： 1.根据实测流速等值线图分析，发现渠道以中垂线为中心，两侧流速基本对称，中垂线流速最大；最大流速点位置在水面以下，，最大流速位置在垂线0.6～0.8y/h范围内，底坡改变对此没有影响。 2.通过对不同垂向流速分布公式与试验资料的对比分析，认为抛物线形式和双幂律形式均可反映流速的实际分布，二者相比较，双幂律公式计算结果较抛物线公式计算结果误差小，因此，垂向流速分布规律推荐使用双幂律公式表示。 3.在各国学者横向流速分布规律研究的基础上，本文采用指数分布形式表示横向流速分布规律，通过大量试验资料拟合出流速分布指数公式，确定了公式参数。 4.在建立U形渠道断面流速分布公式的基础上，提出断面流量的计算公式，实例验证计算精度达到标准；同时，利用浮标测流的思路，采用单一浮标在渠道上进行试验，给出浮标系数，试验验证认为浮标法可以用于U形渠道流量测定。 5.分析不同测点流速脉动过程线，发现其基本类似，并具有大小不同的准周期。由实测资料统计的流速概率分布与理论正态分布计算的概率分布基本一致，可以认为三向脉动流速符合正态分布。 6.各垂线量测纵向、垂向水流紊动强度自渠底向水面先减小后增大，纵向紊动强度最大，最小紊动强度不是出现在水面，而是低于自由水面的一定距离，垂向紊动强度的变化规律与纵向紊动强度变化情况类似，横向紊动强度变化幅度较小，水体动量交换较为稳定，纵、横向相对紊动强度接近为恒定值。 7.垂向雷诺切应力随水深变化比较均匀，近似为恒定值，在坐标轴左右变化幅度较小，纵向与横向雷诺切应力在y/h＞0.5范围内近似为直线，y/h＜0.5区域内近似为三角形分布，横向雷诺正应力沿水深分布比较均匀，近似为线性变化，不同测线上相同水深点横向雷诺正应力数值较为接近。
[Abstract]:The flow of rivers, channels and hydraulic tunnels with free surface is called open channel flow, and the uniform flow of open channel is the most basic problem in hydraulic calculation of open channel. It is widely used in practical production because of its advantages of strong sediment transport ability, superior external force resistance, small area, etc. In view of the particularity of its wide application time and cross section shape, The research on hydraulic characteristics of U-shaped channel is not perfect because of the complexity of flow conditions. In this paper, three kinds of U-shaped channels with different geometric sizes are taken as the research object, and the hydraulic factors such as flow rate, water depth, bottom slope are taken as variables. The flow velocity of the channel under different flow conditions is tested, the velocity distribution of the channel section and the turbulent characteristics of the channel section are analyzed, and the calculation method of the channel flow is explored. The main conclusions are as follows:. 1. According to the analysis of the measured velocity isoline, it is found that the center of the channel is the middle vertical line, the velocity of the two sides is basically symmetrical, and the maximum velocity of the vertical line is below the water level, and the maximum velocity position is within the range of 0.6 ~ 0.8yr / h of the vertical line. The bottom slope change has no effect on this. 2. By comparing different vertical velocity distribution formulas with experimental data, it is concluded that the parabola form and the double power law form can reflect the actual velocity distribution. The calculation result of double power law formula is smaller than that of parabola formula, so the vertical velocity distribution law is recommended to be expressed by double power law formula. 3. On the basis of the research on the law of lateral velocity distribution of scholars in various countries, the paper uses the exponential distribution form to express the law of transverse velocity distribution, and through a lot of experimental data fitting out the formula of velocity distribution index, determines the formula parameters. 4. On the basis of establishing the velocity distribution formula of U-shaped channel section, the calculation formula of section discharge is put forward, and the calculation precision is verified by an example. At the same time, using the train of thought of buoy to measure current, a single buoy is used to carry out the experiment on the channel. The buoy coefficient is given, and it is proved that the buoy method can be used to measure the flow of U-channel. 5. By analyzing the velocities pulsation process lines at different measuring points, it is found that they are basically similar and have different quasi-periods. The probability distribution of velocity calculated from the measured data is basically consistent with the probability distribution calculated by theoretical normal distribution. It can be considered that the three direction pulsating velocity accords with the normal distribution. 6. The vertical turbulence intensity of vertical flow decreases first and then increases from the bottom of the channel, and the maximum longitudinal turbulence intensity is observed. The minimum turbulence intensity does not appear on the water surface, but is lower than a certain distance from the free water surface. The variation law of vertical turbulence intensity is similar to that of longitudinal turbulence intensity. The change of transverse turbulence intensity is smaller, momentum exchange of water body is more stable, and the relative turbulence intensity is close to the constant value. 7. The vertical Reynolds shear stress varies uniformly with the water depth and is approximately constant, and the magnitude of the change is relatively small at the left and right of the coordinate axis. The longitudinal and transverse Reynolds shear stress is approximately a triangle distribution in the range of y / h > 0.5, which is approximately within the region of y / h < 0.5, and the vertical Reynolds shear stress is approximately a triangle distribution in the range of y / h > 0.5. The transverse Reynolds normal stress distributes uniformly along the water depth and is approximately linear. The transverse Reynolds normal stress values at the same water depth points on different measuring lines are close to each other.
【学位授予单位】：西北农林科技大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TV133

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