Geometric Tortuosity Calculation Model of Pebble Formation Considering the Inclination Angle and Shape Characteristics of Pebbles
The tortuosity is an important parameter that responds to the seepage characteristics of soil, and is essential for studying the flow characteristics of fluids inside the soil, but most of the current studies are directed to the study of general models, which are more difficult to apply to the more characteristic pebble strata. In order to investigate the model of tortuosity calculation applicable to pebble strata, the pebble particles are simplified into ellipsoidal shape, the obstruction coefficient and anisotropy coefficient are introduced to describe the arrangement of pebble particles, the characteristic particle size and the ratio of long and short axis of pebbles are introduced to describe the particle gradation and shape characteristics of pebbles. Simplifying pebbles into ellipsoidal particles by obstruction a model is established based on the laminar flow of Newtonian fluid in the pebble stratum, considering the pebble arrangement, particle gradation and shape characteristics, and a formula for calculating the tortuosity is derived. The model of pebble stratum was established based on the programming, and the numerical solution was carried out by the creeping flow module of COMSOL Multiphysics, and the theoretical calculation results were verified with the numerical simulation results;based on the numerical simulation, the influence of pebble inclination on the meander degree was further investigated, and the influencing factors of the meander degree of pebble stratum were parametrically analyzed. The results show that the theoretical model fits well with the numerical simulation and is applicable to the pebble stratum; the tortuosity of the pebbles is the smallest when the pebbles are of equal grain size, and with the gradual flattening of the pebble particles and the increasing of the obstruction angle of the pebble stratum, meanwhile, the tortuosity increases with the increase of the anisotropy coefficient, which indicates that the fluid flows into the pebble stratum from different directions with different tortuosities.
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