2-DIMENSIONAL SIMULATION OF PRESSURE PULSES IN BLADE GAP FORMERS

A numerical, two-dimensional model has been developed to predict press ure pulses created by a blade in gap formers. The equilibrium equation s of the top and bottom fabrics have been solved by finite difference methods. The Navier-Stokes equations and Darcy's Law were used to mode l the flow between and through the fabrics. These equations have been solved by a control volume method using the FLUENT computational fluid dynamics software package. The model predicts that upstream of the bl ade there is little between-fabric variation in pressure. The magnitud e of the pressure here is almost the same as that predicted by the one -dimensional model of Green and Kerekes. Downstream of the blade, the present model predicts a suction pressure on the bottom fabric, in agr eement with the two-dimensional potential flow model of Zahrai and Bar k. The model also predicts, as does the one-dimensional model, that th e influence of viscosity on the pressure pulses is negligible. Owing t o the model's ability to predict the two-dimensional, viscous flow bet ween forming fabrics, we were here, for the first time, able to predic t the shear rate distribution in the fibre suspension. This shear rate distribution, when combined with a model of fibre and floc deformatio n, will allow us to predict the motion of pulp fibres during their pas sage over one forming blade.