Experimental Study On Non-uniform Sediment Incipient Motion & Sand Dune Evolution And Corresponding Turbulent Characteristics

By experimental studying on the interaction of non-uniform sediment incipient motion and sand dune evolution and the corresponding turbulent characteristics, we disclosed the discipline of the dynamical process of the motion of sediment and the corresponding flow, which can afford some experimental data for more extensive study on the river dynamic process.In this experiment, non-uniform sediment is loaded on the bottom of the flume, and then the current condition is adjusted. In the first, using ADV(the Acoustic Doppler Velocimeters), we measured the instantaneous velocity process of several points on the plumb line of a representative section before and after the incipient motion of sand. After a period of bed deforming, sand dunes emerged and we also measured the instantaneous velocity process of several points on the prearranged plumb lines of a representative sand dunes. In the second, by using the tools of turbulence statistical theory, the fluctuation components is separated form the collected instantaneous velocities, and statistic parameters of open channel turbulence are calculated and analyzed, including fluctuating intensity, turbulent kinetic energy, Reynolds stress, probability density, skewness coefficient, kurtosis coefficient, correlation coefficient and integral scale. Finally, using the above acquired data, we drew graphs which can directly reflect the turbulence fluctuation process.During studying the non-uniform sand incipient motion, comparison and analysis methods are adopted in the discussion of the flow structure evolution before and after the sand incipient motion and of the sand motion's effect on the turbulent structure. When researching the course of sand dune evolution, we firstly observed the physical course of the river bed deformation, and then through comparing turbulence statistical characteristics of each point on the same plumb line and comparing those of each point on the different plumb line of a representative sand dune, we concluded the characteristics of the corresponding turbulence in the course of sand dunes evolution.Besides, this study also find the turbulence bursting phenomenon on the sand dunes, and the periodical coherent structure at the dune's trough, and also make a plain analysis about the micro-dynamic process of sand dunes evolution.