Research On The Sedimentation And The Motion In Jets Of Long Particles

This thesis is mainly about the sedimentation of cylindrical particles and the motion of cylindrical particles in jets. The thesis can be divided into three parts.In the first part, the D2Q9 model of Lattice Boltzmann method is used to simulate the sedimentation of circular and elliptical particles in two dimension channel. The sedimentation of two circular particles shows some periodicity, and the initially later particle will accelerate in the wake of the other particle. When Reynolds number decreases, the sedimentation goes through three types of state. Both the initially relative position of the two particles and the width of the pipe don't change the characteristics of the sedimentation. The sedimentation of two elliptical particles with a special initial distribution shows that, when Reynolds number is small enough, the two ellipses keep rotating while sedimentation. When Reynolds number is large enough, the ellipses will reach static position and orientation quickly. For the moderate Reynolds number, the ellipses may get static sedimentation after somersaulting once or several times, or they may got a reverse rotating velocity and may somersaulted reversely. The sedimentation of many elliptical particles with no-slip and periodic wall boundary conditions shows that the ellipses' will tend to get horizontal orientation for both conditions. The average sedimentary velocity under no-slip wall condition is largely less than that under periodic wall boundary condition.In the second part, the D3Q15 model of Lattice Beltzmann method is used to simulate the sedimentation of cylindrical particles in infinite long rectangular- section channel. The simulation of sedimentation of a single cylindrical particle with an initial angle of n/4 with the direction of gravity shows that the sedimentation is affected by inertia and the wall. The wall effect is larger for the narrower pipe and smaller inertia. For weak wall effect, the fiber will reach horizontal orientation. While for strong wall effect, the fiber's position will vibrate about the middle line of the channel and fiber's axis vibrate about vertical orientation, which is the same as the sedimentation of a single ellipse in a two dimensional channel. The simulation of sedimentation of two and many cylindrical particles shows that collisions of fibersoccur frequently and sedimentation is complex. The inverted "T" structures formed by two or more fibers appear and disappear continuously. Generally, when the inertia is large and concentration of suspension is low, the sedimentation shows such characteristics as that of a single fiber. A static inverted "T" structure is got in experiment of the sedimentation of two cylindrical particles.In the third part, the flow of time-developing jets is simulated numerically with the three-dimensional vortex method. Then the motion of suspended cylindrical particles in the jets is calculated with Lagrange model. The results with different Re number, particle Stokes number and particle ratio aspect are given. The conclusions are reached that the particles keep in the jet region when they move in the jets, the particles with initial homogeneous distribution and random distribution of orientation will tend inhomogeneous and preferential orientation with the development of flow. The particles show more homogeneous distribution and more random distribution of orientation in the case of smaller Re number and larger particle ratio aspect. For the case of larger St number, the particles distribute more homogeneously and have preferential orientations more obviously.