Einstein’s viscosity formula is sometimes strongly limited for viscosity estimation of suspensions; that is, it is only applicable for low-concentration suspensions in which hydrodynamic interactions are sufficiently negligible. In particular, hydrodynamic interactions between particles should be taken into consideration when finite-size particles are suspended. Therefore, change in the microstructure, i.e., spatial arrangement of particles in the flow field, is important for understanding mechanism of suspension rheology. In order to provide better practical applications for viscosity estimation instead of Einstein’s formula, the influence of each particle’s contribution on the total effective viscosity of a suspension was investigated for finite-size particles considering the microstructure. Two-dimensional pressure-driven flow simulations including aligned particles or non-homogeneously dispersed particles were performed using the regularized lattice Boltzmann method and a two-way coupling scheme. The rigid circular particles suspended in a Newtonian fluid were assumed to be neutrally buoyant and non-Brownian. As a result, it was found that both distances between particles and particle-wall are significant for viscosity estimation. The results also indicated that the relative viscosity can be estimated accurately when the confinement is sufficiently low (C = 0.04). Moreover, the relative viscosity of the low-concentration suspension under a high Reynolds number condition showed the remarkable thixotropic behavior due to changes in the microstructure, and the viscosity estimation method considering the microstructure is more applicable than Einstein’s formula. It was also suggested that the viscosity estimation method proposed here has application limits at high concentration condition. It can be stated that the microstructure of the suspension is one of the promising factors to estimate and control suspension rheology.

　【卒業論文】

　“微小流路内の粒子の半径方向位置が流体力および実効粘度にもたらす影響の数値解析”，京都工芸繊維大学，2020年2月．

　【修士論文】

　“Numerical study on the microstructure and viscosity estimation of a suspension flow in a microchannel”，京都工芸繊維大学，2022年2月．

　【学術論文】

1. Naoki Okamura, Tomohiro Fukui, Misa Kawaguchi, and Koji Morinishi, "Influence of Each Cylinder's Contribution on the Total Effective Viscosity of a Two-dimensional Suspension by a Two-way Coupling Scheme", Journal of Fluid Science and Technology, vol. 16, no. 3, 0020, pp. 1-13, 2021.

　【国際会議発表】

1. Naoki Okamura, Tomohiro Fukui, Misa Kawaguchi, and Koji Morinishi, "Viscosity Estimation of a Two-dimensional Suspension Flow in a Narrow Channel by a Two-way Coupling Scheme", 18th International Conference on Flow Dynamics (ICFD 2021), Sendai, Japan, 27 - 29 October, 2021, Conference proceedings, pp. 469-470.
2. Naoki Okamura, Tomohiro Fukui, Misa Kawaguchi, and Koji Morinishi, "Fundamental Study on the Total Effective Viscosity of a Suspension Estimated from a Summation of Each Particle’s Contribution by a Two-way Coupling Scheme", 17th International Conference on Flow Dynamics (ICFD 2020), Sendai, Japan, 28 - 30 October, 2020, Conference proceedings, pp. 343-344.

　【国内会議発表】

1. 岡村直希，福井智宏，森西晃嗣，“微小流路内の粒子に作用する流体力の数値解析”，日本機械学会 関西学生会 2019年度学生員卒業研究発表講演会，DVD-ROM，京田辺，2020年3月．

　【受賞】

1. 学生表彰，京都工芸繊維大学，2020年3月．