Research On The Turbulent Fiber Suspensions Flowing Though A T Shaped-channel And A Contraction

The motion of fiber in complex flow of dilute fiber suspensions is simulated numerically by using the slender-body theory and Fluent for fluid and Lagrangian model for particles. This thesis simulates numerically the movement of thousands of fibers, and finally, gets the macro properties of fiber suspensions. The effects of several important parameters of the fiber and flow on the fiber spatial distribution and orientation are studied.In T-shaped branching channel, when the flow was laminar, the movement of fibers is computed by Jeffery equation, supposed the fiber was inertialess rigid cylinder particle. The simulated results are consistent qualitatively with the experimental data available in the literature. The results show that the spatial distribution of fibers is dependent on the fiber aspect ratio. The longer fibers appear infrequently near the upper wall; otherwise the shorter fibers are distributed uniformly. The content ratio of fibers near the upper wall increases monotonically with increasing Re number, and the situation is reverse for the region near the bottom wall. The fibers near the wall align along the flow direction at all times, but the fibers in the central region of the channel tend to align along the flow direction only in the downstream region. When the flow is turbulence, Stokes force brings main effects on the fibers as the Re numbers increased, and Reynolds Stress Model (RSM) for fluid. The results reveal that the diffusion of particle concentration is influenced by the fluctuation of velocity. The particle with low concentration diffuses swiftly in the region of strong fluctuation. The particle with high concentration diffuses slowly in the region of weak fluctuation. The diffusion of rotation is concerned with shear velocity. The particles have large angle and optimal orientation in the region with large curve flow stream. The particle aligns with the flow stream when the flow stream is flat. The orientation of fiber distributes uniformly is influenced by the turbulence pulse.In the contract field, calculate the 3D fluid dispended RSM, produce turbulence with the random-walk method, compute the force on the fiber with 3D subsection integration, solve the equation of the fiber movement using Euler 4 parameters. The result shows that the fiber orientation is concerned with the contract ratio and fiber length. The fiber aligns with the flow stream with large contract ratio. The fluctuation has little effect on long fiber, and the orientation is close to zero. The additional shear and normal stress of fiber become large with the addition of the contract ratio.Including the effect of fiber stress, the flow field is recalculated. The result demonstrates that the fiber with large concentration increases the turbulence dissipation and the pressure loss.