Flexible discretization technique for DEM-CFD simulations including thin walls

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The discrete element method (DEM) coupled with computational fluid dynamics (CFD) method is regarded as a standard approach for a simulation of a gas-solid mixture system. In the DEM-CFD method, the local volume average technique is employed, and hence the fluid motion is calculated based on the void fraction. Although the accuracy of the DEM-CFD method has been improved through lots of studies, inflexibility may become a problem due to the local volume average technique. Specifically, calculations of a gas-solid flow involving thin walls is substantially impossible even by the improved DEM-CFD method. This is because the thin wall cannot be represented when its thickness becomes as large as one grid size due to usage of the local volume average technique. In order to solve this problem, a flexible discretization technique is newly proposed, where the signed distance function and the immersed boundary method are introduced into the dual grid model. In this technique, two kinds of grids are used to calculate the void fraction and the fluid flow. Thus, this technique makes it possible to simulate a gas-solid flow involving a thin wall. Verification and validation tests are performed to show the adequacy of this technique. Through this study, the proposed technique is illustrated to reproduce the exact solution and experimental results in the gas-solid flow involving the thin wall. Consequently, the proposed technique is shown to yield reasonable results in gas-solid flows involving the thin walls.