Research On The Motion Of Particles In The Pipe Flow Of Fiber Suspensions

Pipe flow of fiber suspensions can be found in various industrial processions, such as the production of composite materials, environmental engineering, chemical engineering, paper making, and so on. The character of fiber suspension will play an important part in the quality of the production. So, it is significant to research on pipe flow of fiber suspensions. On the slender body theory, this thesis simulated numerically the movement of hundreds of fibers in pipe flow, and finally, got the macro character of pipe flow of fiber suspensions.Firstly, when the pipe flow was laminar, the movement of fibers was computed in the 2-D force formulae that were deduced from the slender body theory and in 3-D integral method. Results revealed that angles between fibers' axis and the orientation of flow would concentrate gradually on a low number as the Re numbers increased. That is, the axis of fibers would rotate toward the orientation of flow. And this numerical result is similar to the experimental result. Then, the computation was played on different domain, rate of fibers and St numbers and got the conclusion that the farther the distance between the domain and the center of the pipe was, the more fibers' axis concentrated on the orientation of flow, while the rate of fibers and the St numbers had little influence on the distribution. Therefore, we can conclude that the velocity gradient of fluid around a fiber is the key for its rotation.In the next part, after verifying the simplified computational method of turbulence, the movement of fibers in turbulent pipe flow was simulated by 3-D integral method and simplified computational method of turbulence. It was found that the fluctuation of turbulence caused random of fibers' orientation and its distribution became broader as the Re numbers increased. The fluctuation of the fibers' velocity and angular velocity was considered, too, and the influence of flow velocity on them was obvious: the fluctuation intensity of fibers' velocity on flow direction was larger than that on cross direction, while it was opposite for the fluctuation intensity of fibers' angular velocity. Finally, fibers' position distribution on the radius of pipe was counted, and it was obvious that the increase of Re numbers spurred fibers' position diffusion.