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December 29, 2017, 05:28 

#21  
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A. Min
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please introduce me a reference to see this curve (cfl=f(Re_h)) and how to obtain that. Also, what's the meaning of "recovering the constraint due to only the cfl value" ? 

December 29, 2017, 05:50 

#22 
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Filippo Maria Denaro
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That is a classical issue in CFD and numerical analysis and requires the use of the von Neumann analysis. Many texbooks give details about that.
An example for a 2D case is shown in https://www.researchgate.net/publica...ydriven_flows 

December 29, 2017, 05:55 

#23  
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A. Min
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December 29, 2017, 22:40 

#24  
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Arjun
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About the Rhie and Chow term, which is difficult to find from books as to what my comment was talking about here is very short hint. Rhie and chow term is inversely propertional to diagonal of momentum matrix. Diagonal of momentum matrix is inversely propertional to time step size. For euler time stepping it would be ( density * volume / delta_T ). So when delta goes to 0, it shall go to infinity and 1/Ap goes to 0. So basically as delta_T reduces the Rhie and Chow term becomes weaker and weaker. After certain value, it could be too small at some parts of simulation that solution can diverge. 

January 9, 2018, 00:36 

#25 
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A. Min
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Hi all
I want to solve the flow around the cylinder in viscoelastic fluid. At first I did it for Newtonian fluid in Re= 10 , 40 , 100 and for viscoelastic fluid in Re= 10 , 100 and obtained exact results. But when I change the Re to 40 for viscoelastic fluid, it became diverged! I changed many parameters of solution: urf = from 0.1 to 0.9 > diverged! corunt Nu. = from 0.1 to 0.9 > diverged! changing the kind and size of mesh > diverged! changing the kind and size of mesh > diverged! increasing the number of solving pressure correction Eqn from 2 to 20 > diverged! decreasing the min residuals to 1e8 > diverged! changing discretization schemes of div terms: Gauss linear (central), Gauss upwind(1st), Gauss upwind(2nd), limitedLinear , QUICK > diverged! But I have done some ways to solve that: 1 I saw in this page that sb proposed to the other that decrease the residuals to 1e19 !! I did it and my solution became converged! I can't analyze that! Is it possible? 2 In the other way I increased the number of solving pressure correction Eqn to 20, decreasing the min residuals to 1e8 3 setting the time step to 0.001 instead of setting Cr=0.3 Now I don't know that my results are reliable or not! Could you please tell me what happend that these solutions are appropriate for solve it? Thanks 

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time step size, transient 
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