Research Of Roughness Coefficient And Turbulence Character In Uniform Flow Of Open Channel

The hydraulic calculation of the uniform flow is the most fundamental problem of the open channel and its variation law is the basis of the analysis in the open channel. The roughness coefficient as an important parameter is very critical and useful to the hydraulic engineering whenever on the stage of design, construction, operation and management of the project. The major object in this article is uniform flow in the rectangle open channel. In order to obtain the variation law of the roughness coefficient and the turbulence intensity, the experimental research is on the basis of the friction law and turbulence character under the smooth wall and three different artificial rough-walls. The three-dimensional velocity can be measured through the ultrasonic velocity device of Nortek Vectrino+, so we can discuss the distribution of the three-dimensional relative turbulence intensity. In the article there are some results can be deduced as follows:1. In the uniform flow of open channel, the roughness coefficient isn't a constant under the same condition of the artificial rough-wall, which can increase when the discharge decreases and the width-depth ratio increases. The roughness coefficient increases when the relative roughness of the surface becomes larger under the same condition of discharge. Then the relationship of the roughness coefficient and the Froude number can be expressed the same index law even under the different artificial rough-walls, and the roughness coefficient increases with the larger Reynolds number.2. In order to obtain the calculation formula of the roughness coefficient under the experimental conditions, the relationship of the hydraulic parameters between the open channel and circular pipe is assumed. Then through the comparison and analysis, the formula is obtained with the average deviation of 3.02%.3. The distribution of the average velocity under the condition of the hydraulic smooth wall is coincident with the logarithm distribution and in this situation, the Karman parameter is 0.4875 which is a little larger than 0.4 in the Nikuradse experiment of circular pipe. And the distribution of the average velocity in the rough-wall is coincident with the logarithm distribution. The cross distribution of the average velocity indicates that the increase of the roughness coefficient make the distribution of velocity more uniform. 4. The variation law of the turbulence intensity is that, it increases when the y h ?decreases under the condition of the same wall and discharge, and it increases when the discharge increases under the condition of the same wall and y h . The variation law of the relative turbulence intensity, which is the ratio of the turbulence and the major average velocity, can be described as follows: under the smooth wall condition there are three different zones in the relationship of relative turbulence intensity and two different zones under the rough wall condition. In the major zone, the relative turbulence intensity increases when the y h decreases under the different walls. The maximum measured points all locate the point of y h = 0.2, and the maximum of the relative turbulence intensity increases when the wall is rougher.5. The boundary shear and friction velocity have the variation law in common, which is that, they increase when the discharge increases under the same condition of walls, and increase with the rougher wall under the same condition of discharge. In the experimental research, the range of the boundary shear is 0.804-1.205 N m 2and the range of the friction velocity is 0.028362-0.034737m s .