Influence Of Different Roughening Forms On Channel Discharge Capacity

Hydraulic model test is an important way to study and solve practical hydraulic engineering problems,and model roughening is the main method to study resistance similarity.In nature and practical engineering,the bed surface of open channel has different forms and scales of roughness.Artificial roughening is one of the ways to study the roughness of channel.Therefore,it is of great theoretical and practical significance to study the hydraulic characteristics of channel through several different roughening methods.Most of the previous roughening experiments put the roughened body in the main channel to study the change of roughness.In this thesis,by roughening the side walls on both sides of the trapezoidal channel,the changes of hydraulic factors without roughening and three roughening forms are studied and analyzed,and the following results are obtained:(1)Based on the measured experimental data,the distribution law of time average velocity under different rough conditions is studied.The results show that the time average velocity distribution on each vertical line is regular,which is not only related to the layout of the roughness,but also related to the size of the roughness.The time average velocity of quincunx roughening is less than that of rectangular roughening,and quincunx roughening has better water blocking effect;When the roughness size becomes larger,the time average velocity of the corresponding measuring point becomes smaller.Comparing the logarithmic fitting formula with the parabola fitting formula,it is found that the parabola formula can better fit the vertical formula when the flow is small and the water depth is large.(2)In the uniform flow in open channel,when the channel section shape and roughness are unchanged,the roughness value is not an invariable constant,which will increase logarithmically with the increase of water depth and decrease with the increase of flow;For the wall with different roughness,the roughness value of quincunx roughness is greater than that of rectangle;The volume of roughness becomes larger,and the roughness value becomes larger accordingly.(3)The correlation between roughness value and hydraulic factors is analyzed.It is found that the roughness value has a weak correlation with the change of flow.The main factors affecting roughness are the layout of different sizes of roughness and the change of water depth.(4)The variation laws of turbulence intensity and turbulence kinetic energy under different flow and roughness conditions are studied.It is found that the longitudinal turbulence intensity is the largest and the transverse turbulence intensity is the smallest on the same velocity vertical line;The longitudinal turbulence intensity is larger near the channel bottom,which first decreases and then increases along the water depth direction.The longitudinal turbulence intensity in quincunx roughening is greater than that in rectangle,and the flow is more stable without roughening;When the roughening method is fixed,the water depth remains unchanged,and the longitudinal turbulence intensity increases with the increase of flow.When the flow is constant,the water depth remains unchanged,and the transverse turbulence intensity with large volume of rough body is larger.The variation law of turbulent kinetic energy along water depth is the same as that of longitudinal turbulence intensity.(5)The changes of wall shear stress and friction velocity are analyzed.It is found that the wall shear stress and friction velocity will change with the test design variables.Under the same flow condition,the coarser the wall,the greater the wall shear stress and friction velocity,indicating that the roughness value will also increase with the increase of wall shear stress.