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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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Initial velocities of free-settling spherical particle
Chára, Zdeněk ; Kysela, Bohuš
The paper deals with experimental research of the initial phase of free-settling spherical particle which density is close to the density of water. The experiments were carried out with a smooth particle as well as with a particle with a rough surface. The obtained results show that in the initial phase of sedimentation, there is a formation of vortex structures, which are reflected in the increase of resistance in coefficient values.
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Pohyb kulové bubliny v okolí padající kulové částice
Vejražka, Jiří
This report focuses on a motion of a small spherical bubble, which rises in a still liquid particle and encounters a falling spherical particle. We consider the case of very small bubbles and of relatively large particle (whose size is much bigger compared to the bubble). The report provides expressions for forces acting on the bubble and equations for the bubble motion. The motion equations form a system of ordinary differential equations, which should be solved numerically. The purpose of this study is to provide a mathematical model, which would describe experimental observations by Hubička et al. (2009). In these experiments, a decrease of collision efficiency of the flotation process is observed if the particle is moving, compared to the case of still particle.
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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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Výzkum odporové síly a točivého momentu rotující koule pohybující se v klidné vodě
Kharlamov, Alexander ; Kvurt, Y. ; Chára, Zdeněk ; Vlasák, Pavel
The paper describes results of experiments with rotating spherical particles moving quasi-steadily in the calm water. The motion of the particles was recorded by a digital video camera. The Cartesian coordinates and the angle of rotation of the particles were determined from the record of the particles motion. The dimensionless drag coefficient, drag moment coefficient and translational and rotational Reynolds numbers were calculated from the time series of the particles coordinates and angle of rotation for each recorded frame. The effect of the particles translational motion on the drag moment and the effect of the particles rotation on the drag force were evaluated from the experimental data.
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Experimentální výzkum odporu rotačně se pohybující kulové částice
Lukerchenko, Nikolay ; Kvurt, Y. ; Chára, Zdeněk ; Vlasák, Pavel
Saltatory solid particles conveyed by fluid impact a channel bed from time to time. As a result of the collision the particles receive angular velocity, which gradually decreases with time. For numerical simulation of saltation it is necessary to know values of the drag rotation coefficient. In this paper experimental results of the rotating spherical particles moving in water are described. The rubber spherical balls with density near that of water were used; each of them was speeded up in a special chute that ensured that the particle rotated in a given plane. Values of the drag coefficient of the rotating spherical particle were determined in a dependence on rotation particle Reynolds number
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