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Transition from the saltation mode of bed load transport to the rolling mode
Lukerchenko, Nikolay ; Ivanova, Irina ; Chára, Zdeněk ; Vlasák, Pavel
The paper deals with the sediment transport of sand particles conveyed by water in an open channel. A 3D numerical model developed by the authors was used for simulation of the sand particles movement in the channel with rough bed. Similarly to Shields theory of sediment transport incipient motion of the bed load particles the shear stress for the transition process from saltation mode to rolling mode can be defined. The shear stress value can be determined as a function of two dimensionless parameters, particle parameter and equivalent bed roughness. The particle parameter is a function of the particle size and density, and the carrier liquid density and viscosity. The presented numerical solution reveals that the shear stress for the transition process from saltation mode to rolling mode is less than the shear stress for the incipient sediment motion and depends on channel bed roughness.
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Zahájení pohybu dnových sedimentů v režimu saltace
Kharlamov, Alexander ; Chára, Zdeněk ; Vlasák, Pavel
The paper deals with dependence of threshold shear stress on Reynolds number for saltation mode of bed load transport. The incipient of particle saltation in turbulent flow was determined and presented in variables introduced by Shields. For the condition of the threshold there was chosen the equality of the submerged gravitational force and the lift force on a bed particle. An additional dimensionless parameter ξ characterizing the bed surface formation was introduced. The critical shear stress as function of bed particle Reynolds number was determined analytically and reported in graphical form for different values of the bed parameter. The calculated values of an introduced parameter ξ characterising bed formation differ from results of Ling (ξ=3) and approximately agree with experimental results of Ancey et al. (ξ=2/3).The obtained results agree with available experiments on saltation start.
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Numerický model saltace kulovité částice v kanále s příčně skloněným drsným dnem
Lukerchenko, Nikolay ; Piatsevich, Siarhei ; Chára, Zdeněk ; Vlasák, Pavel
The paper deals with 3D numerical model of the spherical particle saltation in the rectangular channel with rough bed and the effect of lateral slope of the bed. The stochastic method based on the concept of contact zone is used for the calculation of particle-bed collision. Some examples of calculation are presented, in particular, the effect of transverse tilted bed on the particles sorting. The beams of the trajectories of particles starting saltation from one point are calculated. The centrelines of the beams can be approximated by straight lines for low and moderate values of the bed transverse slope and the angles between centrelines and the stream direction depend on the lateral slope of the bed.
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2D numerický model dna kanálu utvářeného náhodně rozdělenými kulovitými částicemi
Kharlamov, Alexander
The paper deals with the saltation mode of bed load transport. The saltation process modelling consists of two parts – deterministic motion of the particle in fluid and stochastic process of its collision with bed, which is the stochastic part of a Monte-Carlo simulation. The channel bed is formed by spherical particles of non-uniform size, the distribution of the particles radiuses and the particle height is of Gaussian type. The numerical method of a bed forming and determination of collision coordinates and a collision angle is proposed.
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Výpočet funkcí parametrů saltačního procesu
Piatsevich, Siarhei ; Lukerchenko, Nikolay ; Chára, Zdeněk ; Vlasák, Pavel
The results of the 3D simulation of the solid spherical particles saltation in an open channel with rough bed are presented. The dependences of mean saltation length, mean saltation height, mean saltation velocity and mean deviation of angle of particle trajectories with respect to the downstream direction were studied and determined as the functions of the saltation process parameters, such as the flow shear velocity and the particle diameter.
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