Development Of LBM-DEM For Bingham Suspensions With Application To Self-compacting Concrete

Rock-Filled Concrete (RFC) is a kind of concrete that is formed by filling gapsbetween rocks with self-compacting concrete (SCC). This filling/casting process can becharacterized essentially as viscoplastic (or Bingham) suspensions flowing throughporous media. In this thesis, a coupled Lattice Boltzmann method and Discrete ElementMethod (LBM-DEM) is developed using the immersed moving boundary method. LBMis an emerging computational fluid dynamics method, which has attracted widespreadattention since1988. Based on the mesoscopic particulate characteristics, LBM hasmany inherent advantages, including regular grid, high parallelizability, as well asefficient and robust implementation over complex domains. DEM is able to simulatevarious interactions between particles such as collision, friction, and blocking.Therefore, the coupled LBM-DEM, which integrates advantages of LBM and DEM, issuitable for studying the flow of viscoplastic suspensions through porous media.As Bingham fluid is typically Non-Newtonian, the linear collision operator that isoften used in Newtonian fluid needs to be modified. In this thesis, the Papanastasiou’smodel is used instead in order to avoid the discontinuity of the standard Bingham model.As a result, a new parameter m is introduced. When m is set to be large, the calculationof LBGK becomes instable. Hence the multiple-relaxation-time lattice Boltzmannmodel (MRT-LBM) is used to overcome this problem. In this work, MRT-LBM is usedto study Bingham flow in various2D and3D channels. In addition to the rich flowstructures, the dynamical forces on the round or spherical particles are calculated.Results show that both the Reynolds number Re and the Bingham number Bn affect thedrag coefficients CD, based on which a comprehensive equation that considers theeffects of Re and Bn on the drag coefficient is proposed.Building on the above work, a viscoplastic LBM-DEM framework is developed tostudy viscoplastic suspensions flowing through channels with a single gap and porousmedia in2D. In the first case, the effects of aperture ratio, solid particle holdup andpressure gradient on the blocking of viscoplastic suspensions at the gap are quantifiedusing the passing factor, which describes the risk of blocking. It is found that the keyfact that controls blocking is the aperture ratio. The critical aperture ratio is2, belowwhich the risk of blocking sharply increases. As the solid particle holdup increases, blocking becomes easier. However, the pressure gradient has no impact on thesuspensions’ blocking. In the later case, it is found that viscoplastic suspensions are ableto ‘find’ the wider gaps automatically. As a result, the flow is divided into the ‘mainstream’ and the ‘branch stream’. The risk of blocking increases significantly as thenumber of narrow gaps increases. Finally, viscoplastic suspensions flowing throughporous media in3D is studied. Not only are the rich flow structures obtained inside theporous media that can not be easily observed in physical experiments, the motion andblocking of particles in viscoplastic suspensions are also simulated successfully. Theresults prove that the viscoplastic LBM-DEM is a powerful and efficient numericalmethod to study the mesoscopic mechanisms of SCC’s casting process.