
Doubts Regarding Flow Over a Cylinder Results
Hello everyone,
I have just completed the assignment for flow over a cylinder, and I’ve explored different approaches and methods to understand the differences.
I utilized the “Pseudo Transient Approach” and the “Under Relaxation Factor” and compared residuals and iteration numbers. As expected, the iteration numbers increased with decreasing time step size and under relaxation factor, which doesn’t pose any problems.
However, I encountered difficulties while creating the mesh and achieving convergence with the SIMPLE method. Here are some questions I’d like to address:
1. How can we prepare a 2D domain in Fluent Mesher? Is it possible, or do we need to introduce some thickness into the geometry? (I managed to prepare a 2D domain using the Workbench Mesh.)
2. I attempted to calculate turbulence intensity and reference length, but I have doubts about using the correct numbers. In the assignment, the cylinder diameter was 1 meter, and the inlet velocity was 50 m/s. Consequently, the Reynolds number is 4.975E7, and turbulence intensity, I = 0.0175. So, if turbulence intensity is 1.75% and the reference length is 1 meter, am I correct? If I wish to use turbulence intensity and hydraulic diameter, will the values remain the same? By using the calculated values, the default iteration number decreased from 533 to 441. Yet, there are slight differences in pressure values and streamlines (Figures attached). How can I determine which is closer to the real situation?
3. I wanted to employ the SIMPLE method to utilize under relaxation factors, but I couldn’t achieve a converged solution with “Second Order” Pressure Discretization. Changing it to “PRESTO!” led to convergence, but I’m unsure why this alteration worked. Can you explain the differences? Given the multitude of options, is there a source I can consult to understand the distinctions between these or any other methods?
4. I noticed slight variations in the results of pressure and streamlines when comparing results between the “SIMPLE” algorithm and the “COUPLED” algorithm. How can I determine which one is more stable under specific conditions? Can you recommend a guide or resource to explore this further?
I hope you can see the names of the images. You can differentiate them by their names.
Thank you so much.
Best Regards,
Burak
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