Primary Exploration For The Relationship Between Friction Velocity And Average Flow Velocity Of Unsteady Flow In Open Channel

Open channel steady flow is open channel hydraulic calculation in the most basic problem,it is the important research direction of the fundamental principles of open channel flow,with a constant flow analysis is currently open channel flow of theoretical basis and premise.The main moving elements of unsteady flow can change with time,and its motion is far more complex than that of steady flow.Research on open channel non relative characteristics of unsteady flow is not only conducive to the development of water science,of modern urban river and coastal engineering problem solving has important significance.The research of unsteady flow is more complicated,in order to get the law of motion,it is a combination of theoretical analysis and experimental research.In this paper,a complete test of PIV flow meter for unsteady flow is established.Throughout the test using a high precision of unsteady flow test system,by the inverter to control the speed of the pump generating stable and continuous sinusoidal unsteady flow process,through the electromagnetic flow meter to detect and record the flow,ultrasonic level meter to collect the water level.After testing the system accuracy is high to meet the test requirements.Through the experiment,the flow velocity,water depth,flow of data integrity in the case of unsteady flow in open channel.The data were analyzed,and the relationship between mean velocity and frictional velocity was obtained.Through the theoretical analysis and experimental research work,the following conclusions are drawn:1)In the open channel steady flow,three calculation methods(resistance balance,logarithm of the inverse calculation,vertical Reynolds stress distribution of friction velocity results are compared,with logarithm of the inverse algorithm to calculate the friction velocity values for the most stable,minimum error;vertical Reynolds should force algorithm out value error floating moving too large,need to be selective.2)In the open channel steady flow calculation,mean velocity distribution diagram can satisfy the logarithmic velocity distribution formula,according to the test data,calculate the test the Karman constant values were 0.414,slightly larger than the test commonly used in 0.4.The mean velocity distribution of the time averaged velocity distribution is also consistent with the logarithmic velocity distribution formula in thecondition of unsteady flow.3)In steady stream,the average velocity and the friction velocity is increase with the decrease of the simple relationship.In the phase analysis of unsteady open channel flows,the mean velocity and friction velocity is similar: in the variation of the flow velocity of the short,friction velocity changes more obvious;velocity change the more gentle,friction velocity changes is smaller.4)According to the test data,the relationship between the average velocity and the friction velocity is fitted,and the fitting formula is analyzed.In respectively,and specific than drop,mean velocity and friction velocity as is seen in the single variable control after the unsteady flow turbulent dynamic phenomenon is still evident.