Flow Dynamics Characteristics Around Sediment Particles With Consideration Of Scale Effect

Studying on flow dynamics characteristics around sediment particles withconsideration of scale effect is of great significance to research the movement ofsediment. Scale effect is based on the two aspects: geometric scale and dynamicalscale. From the view of the geometric scale, it can be divided as fine grains and coarsegrains. From the view of the dynamical scale, it can be divided as low Reynoldsnumber and high Reynolds number conditions. This paper investigates the flowstructure around sediment particles briefly considering the scale effect by means oftheoretical analysis, numerical simulation and experimental investigation, especiallyon the following issues:1. For fine grains, the erosion and deposition and flow structure in the perturbedcase by pipe are mainly analyzed.To begin with, based on finite volume method, a vertical two-dimensional (2D)numerical model is presented, formulas of incipient velocity of various sediments,approximate calculation on theoretical scour depths are put forward for pipelines’scour and deposit in the South China Sea for engineering application with theconsideration of effects of incipient velocity, pipe diameter and sediment particle size.Additionally, based on finite difference method, a vertical two-dimensional (2D)numerical model has been performed to do further simulation about flow structure forlocal scour around pipeline, and compare two final results under the disturbance ofdifferent pipes, and the corresponding scour formula is obtained.Finally, this paper obtains sediment transportation, flow field distribution andenergy spectrum through flume experiment on bed evolution resulted by disturbanceof fine grains.2. For coarse grains, the flow structures of the pebbles in different hiddendegrees are analyzed.Firstly, based on finite difference method, a vertical two-dimensional (2D)numerical model has been performed to investigate the flow characteristics of thecoarse grains under linear wave considering longitudinal and vertical hidden degrees.Secondly, based on finite volume method, a vertical two-dimensional(2D)numerical model has been performed to investigate the flows around one or more circular pebbles in meticulous arrangements at high Reynolds number, which givesconsideration to longitudinal and vertical hidden degree, and the rolling model isincorporated to further explore the start rule combined with water flow structure.Comparison numerical results show that longitudinal hidden degree also has arelatively significant effect on hydrodynamic forces factors in view of9cases.Newly, based on finite volume method, a horizontal two-dimensional(2D)numerical model has been performed to investigate flow structure around pebbles atlow Reynolds numbers with numerical analysis via the non-staggered grids. Takinginto account the longitudinal and lateral hidden degree, the flow structure and thedynamic characteristics of vortex around pebbles, lift and drag force are simulatedrigorously considering effects of different Reynolds number and different relativehidden degree.Lastly, flow field distribution, section velocity, turbulent intensity, Reynoldsstress, as well as turbulent kinetic energy around the coarse grains of different hiddendegree in longitudinal and vertical are obtained by flume experiments. Meanwhile,theory and method of EEMD-HHT are employed to study the flow structure, and thecorresponding marginal spectrum, the marginal energy spectrum, the instantaneousenergy spectrum and the total energy are obtained.