Experimental Study On The Relationship Between Roughness Coefficient And Surface Roughness For Uniform Flow In The Open Channel

Hydraulic calculation of open channel flow of the roughness coefficient, is a difficult problem in hydraulic calculation of long unresolved. The change rule and function still inconclusive so far. In this paper, by means of artificial roughness uniform flow channels to test the concrete wall and three different particle size of wall. Study on uniform flow in open channel, the influence degree of channel roughness coefficient under different flow patterns. Analysis and establishment the function relation between open channel flow pattern, wall roughness and roughness coefficient.Roughness value n varies with the flow rate Q has an important relationship with the flow pattern.When Fr>1(the jet flow),the roughness increased with the increase of flow;Conversely,When Fr<1(the slow flow),Roughness value n with the flow rate of Q decreased。With the surface roughness Δ increases, the greater the roughness value n.Under the same flow,The roughness n increases along with the Froude number Fr first increased sharply and then increases slowly,that is when Fr<1,Roughness value n with the Froude number Fr growth line with steep;when Fr>1,The roughness value n with the Froude number Fr growth line.Under different absolute roughness Δ,With the increase of the Froude number Fr, roughness value n first increased sharply and then increases slowly.When Fr<1,the roughness n are related with Froude number Fr and absolute roughness Δ,n=f(Fr,Δ);When Fr>1,The roughness value n is mainly related with the absolute roughness Δ,has little to do with the Froude number Fr,n=f(Δ).Under the same slope i,With the increase of the Froude number Fr, roughness value n decreased in power function. Roughness value n varies with the average water depth h and Reynolds number(Re)has an important relationship with the flow pattern. When Fr>1,the roughness increased with the increase of the average water depth h and Re increases; When Fr<1,Roughness value n with the average water depth h and Re decreased.According to the different particle size of roughness of channel test data to draw n-Fr diagrams,And through the fitting analysis,obtain the roughness Δ and the roughness value n function.and is verified by the experimental data of concrete channels.According to the different bottom slope i channel test data to draw n-Fr diagrams,and through the fitting analysis,obtain the bottom slope i and roughness value n function.and is verified by the experimental data of concrete channels.