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Numerical simulation of detailed flow through forming fabric Wang, Zhishuo

Abstract

The relation between the filament displacement of forming fabric and the wire mark characteristic of final paper product is investigated for the first time. The ultimate goal of this research is to understand the detailed dewatering mechanism of forming section in 3D level as well as provide a guide of forming fabric design and maintenance to obtain paper product with best quality. A 3D computational model of a square weave single-layer forming fabric has been developed by geometry modeling and commercial CFD software to simulate the detailed dewatering process of forming section. The reliability of the geometric model, grid convergence, solver settings, and boundary conditions are checked. Experimental data of wind tunnel screen is used to indirectly validate this model since currently there is no 3D experimental data of forming fabric available. Accuracy analysis is conduct with GCI (grid convergence index) method, which is widely accepted for CFD error estimation. Next, the effect of filament’s displacement on the upstream velocity distribution, which represents the fiber distribution in the formed fiber mat, is revealed. From wire mark theory, this distribution pattern can directly affect the grammage and wire mark level on paper sheet. The 2D/3D velocity plots of geometric structure with filament displacement are compared with those of uniform structure. Pressure drop and mass flow rate under both cases are also discussed. The CFD result shows the displacement of forming fabric filaments has a significant adverse influence on the uniformity of the upstream velocity distribution and mass flow rate through different open areas of the fabric. Good agreement between the simulation outcomes and experimental pressure drop values through wind tunnel screens is achieved. The pressure drop through fabric is independent of the displacement. Therefore, it cannot be used to judge the fabric uniformity. This numerical model can significantly contribute to the understanding of forming fabric with a low cost. However, 3D experimental work should be done in future to validate this model. More complex CFD models such as multi-phase model also should be developed as the next step to obtain more accurate results.

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