Study On The Friction Characteristics Of Unsteady Flow In Open Channel Based On PIV Experiment

Water usually is a constant flow in natural river.In recent years,river unsteady problem increasingly prominent.With the acceleration of construction of water conservancy development and the development of computer technology.The mathematical model and physical model has been greatly used in the study of unsteady flow.Because of the unsteady flow in open channel flow itself is more complicated and restricted by measurements.Many characteristics of unsteady flow in open channel flow research have not been able to have a larger breakthrough.Investigate the friction characteristic of the bed is very important for our understanding of the dynamic characteristics of open channel flow.It has important theoretical and engineering significance in grasp of the correct velocity vertical distribution,unsteady flow in open channel flow propagation characteristics,the development of water conservancy,the port,shipping and solve actual problems such as urban flood control.In order to study the friction characteristics of unsteady flow in open channel flow,this paper based on the PIV experiment,adopt Logarithmic velocity profile method and the traditional velocity distribution model combined with least square to determine the friction velocity and roughness height.Analysing roughness height,friction velocity and drag coefficient variation law of the steady flow and unsteady flow.And than explore the relationship between the two.The main research conclusions are as follows:(1)In an rising limb of unsteady flow,the rough height increase with the passage of time.And the rough height decreases with time when the water go down.(2)Friction velocity of unsteady decreases first and after increases in the unsteady period.Contrary to the change of the rough height.(3)The vertical distribution of changes and have good consistency in each section of steady flow and unsteady.Compared with constant flow,two parameters of unsteady flow twists and turns curve degree higher than a constant flow.The rough height,the change of the friction velocity and has more obvious consistency.(4)The rough height and friction velocity has a good linear relationship in steady flow and unsteady flow.But the linear relationship of unsteady flow is more outstanding.(5)Both steady flow and unsteady flow,the drag coefficient decreases with the increasing of the layer number and water level.And with the increase of the depth of the water,reduce the drag coefficient of variations between layers.