The Study Of Propagating Characteristics Of The Unsteady Open-channel Flow

Unsteady flow is the most common form in natural fluid movement. Flood routing in river,outflow from reservoir,lock filling or lock emptying,tidal wave,sea wave and so on. These are the typical unsteady flow model. Kinematical parameters of unsteady open-channel flow vary with time, which leads its flow more complex than that of steady flow. Limited by research means, study of unsteady open-channel flows has not been developed obviously, but it is of great significance both in theory and in engineering.In this paper, theoretical and experimental research was carried out for studying the propagating characteristics of the unsteady open-channel flow and the vertical distribution law of the flow velocity. The main contents and results are:One high-accurate experimental systems with high accuracy were established here to generate stably continuous unsteady flows with water pump controlled by transducer. The measurement of the discharge was done by electro figmagnetic flow meter, water depth by ultrasonic water level recorder.By studying the propagating characteristics for the unsteady flow, the changing law of wave velocity C 0, flow depth H , discharge Q and deformation rate tu / T were obtained with the experiment executed in 28 meters flume.Propagating velocity of unsteady open-channel flows C 0 can be expressed by flow velocity and micro-wave velocity at wave peak.Water depth is close to H Qmax at flow wave peak and to H Qmin at flow wave bottom for long period unsteady flows. When the period is short, water depth at wave peak and wave bottom are both close to H . Here, H Qmax is the water depth for the maximal discharge which is equal to that for the constant flow of the same discharge, H Qmin is the water depth for the minimum discharge which is equal to that for the constant flow of the same discharge, and H is the averaged water depth of the two depths.Outer enveloping profile of discharge is analogous to that of flow depth for unsteady flow. But the averaged discharge (Q min + Qmax)/2 keeps constant when the flow propagates. And discharge's wave amplitude Qb (x) at exit of flume is the function of unsteady flows'period T and discharge's wave amplitude at the entrance of flume.Wave form of unsteady flow would be deformed when it propagates with the rising stage longer and the falling stage shorter. And the deformation rate tu ( x)/T is the function of distance x , period T and relative discharge's wave amplitude.Propose unsteady parameters which include discharge influence and period influence.