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Collision of a rotating spherical particle with flat wall in liquid
Lukerchenko, Nikolay ; Kvurt, Y. ; Chára, Zdeněk ; Vlasák, Pavel
The collision of the rotating spherical particle with a flat wall in liquid was studied experimentally. The glass and steel beads rotating in water and silicon oil were used. A high-speed video system recorded the bead motion before and after the collision. It was shown that the restitution coefficient depends not only on the Stokes number but also on the particle angular velocity; the restitution coefficient decreases with increasing of the rotational Reynolds number and decreasing of the Stokes number. These results can be useful in modelling of the two-phase flows near solid boundaries.
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Influence of the spheroid prolongation on the drag force
Lukerchenko, Nikolay ; Keita, Ibrahima ; Kvurt, Y. ; Miles, Jiří
The drag force acting on a spheroid moving perpendicularly to its axis of rotation in water was studied experimentally. Along the spheroid axis, which is normal to its axis of rotation, a round narrow hole was bored. The spheroid moved along a thin vertical thread stretched in water. A video system recorded the spheroid motion and the spheroid velocity was determined from the record. The drag force coefficient was calculated from the balance of forces acting on the spheroid. Two oblate, two prolate spheroids and one sphere with ratio of the axes 0.67; 0.81; 1.33; 2 and I (sphere), respectively, with approximately the same volumes, were used. The friction coefficient between the thread and spheroid was determined from the comparison of the experimental and calculated motions of the sphere, for which the drag force coefficient is known. The dependence of the drag force coefficient of the spheroid on the ratio of its semi-axes was obtained.
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Experimental evaluation of the drag torque, drag force and Magnus force acting on a rotating prolate spheroid
Lukerchenko, Nikolay ; Keita, Ibrahima ; Kvurt, Y. ; Miles, Jiří
The drag torque, drag force and Magnus force acting on a spheroid rotating around its axis of symmetry and moving perpendicularly to this axis in initially quiescent water were studied using experimental data and numerical simulation. The prolate spheroid with ratio of the axes 4/3 was speeded up in special device, which ensured the required rotational and translational velocity in the given plane. A video system was used to record the spheroid motion in water. Using the video records the spheroid translational and angular velocities and trajectory of its center were determined and compared with the results of the numerical simulation. The dependences of the coefficients of the drag torque, drag force and Magnus force on the Reynolds number and dimensionless angular velocity were obtained.
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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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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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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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