Dear all,
I have a simple tube with a flowing hot fluid, modeling with Fluent. I want to study the mesh independency study. My question is why output velocity is bigger for coarse mesh?, and it is reduced & converged to a value when I increase the number of cells.
Thanks,
Generally we aim is to get a solution which is independent of the mesh.
However sometimes we have to find a compromise between a fine mesh with very high accuracy and coarser mesh with acceptable accuracy and acceptable computational cost.
Best regards.
Thanks Mounir. I understand that. But, is it normal to have this behavior that a parameter starts to converge from a value and reduces by increasing the number of cells? Or I missed something within my simulation!
To answer this question indirectly, have a look at Upper Riemann sum and Lower Riemann Sum in integration method. You can understand the gap easily, when you are moving from coarse mesh to finer mesh. Almost a similar technique is used in any numerical method which deals with PDE or ODE.
To my opinion, it depends upon number of Gauss Points you chose (or set to a default value in the software) for Integration. Depending upon the number of Gauss Points, your stiffness matrix can be less stiff (under-integration) or it can be too stiff (over-integration).
In short, it depends on Under-integration and Over-integration, whether your displacements will converge from below (i.e.,displacement value increases as you densify the mesh) or from above (i.e., displacement value decreases as you densify the mesh).
Dear Panchatcharam and Rajni,
Thanks for your answers. What you said is logically, but there is no option in ANSYS Fluent to change element integration point, only element orders (linear or quadratic) can be changed.
Dear Mohammed,
I agree with you, my question is why it is converged while the parameter decreases, because for me coarse mesh always provide poor results. Although, based on the integration strategy scheme this reduction behavior can happen, but based on my knowledge there is no option to define the order of integration in Fluent.
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