吸水性粒子の間隙における自由液面流れの数値解析手法

Abstract

本研究では，水を吸収すると膨張する吸水性粒子の間隙に浸入する自由液面流れを有限体積法により計算する手法を提案する．吸水性粒子の膨張により，水に接する粒子の固体領域が広がり，その影響を粒子表面の流速と圧力の境界条件として考慮する．この計算手法を用いて非吸水性粒子間隙の lock-exchange 問題や単一の吸水性粒子の膨張問題を計算し，高密度流体側のフロント位置や水の体積保存性について基本的な検証を行った．さらに，複数の吸水性粒子間隙に浸入する dam-break 流れに対する数値実験を行った．その結果，粒子間隙におけるフローパターンは粒子の膨張に大きく影響を受けること，また粒子の吸水速度が大きくなりすぎると粒子間隙へのフロントの進行が阻害され，領域全体の粒子吸水量が低減する可能性があることを示した．A computational method was proposed for the free-surface flows intruding between multiple absorbent particles on the basis of the finite volume method. In the proposed method, the solid area of the particle, which is in contact with water, expands due to the swelling of the absorbent particle. The influences of particle swelling and water absorption on flows are considered with velocity and pressure boundary conditions on the particle surfaces. The proposed method was first applied to the lock-exchange problem in porous media, which consist of multiple non-absorbent particles. Second, the swelling of a single absorbent particle was calculated with the present method in saturated and unsaturated conditions. The basic applicability of the proposed method was confirmed through the discussions about the front position of the heavy current in the first calculations as well as the volume conservation of water in the second investigations. In addition, the proposed method was applied to the dam-break flows in the porous media, which consist of multiple absorbent particles. As a result of the numerical experiments, it was demonstrated that the flow patterns intruding the porous media are largely affected by the swelling particles. In particular, it was found there is a possibility that the total amount of water absorption decreases due to the blocking of the flows by the swelling particles even in case the water absorption speed of the particles is sufficiently high.