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Ansys Learning Forum › Forums › Discuss Simulation › Fluids › Speedup simulations of laminar flows with low Reynolds number › Reply To: Speedup simulations of laminar flows with low Reynolds number

October 17, 2017 at 5:34 am
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Ansys Employee

You frequently observe that the convergence of the residuals is very good, but the velocity and pressure at monitor points change very slowly on meshes with aspect ratios bigger than 800. This behaviour is caused by the default settings for the ANSYS CFX Solver. The hidden expert parameter: d diffusion option = 3 (1, by default) changes the numerics of the Rhie and Chow algorithm. The effect increases with cell aspect ratio. Note that, as the parameter value of 3 increases the non-linearity, it can cause convergence troubles, e.g. in strong non-Newtonian fluids. Additional keywords: low Re Number, slow convergence