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As can be seen, the Strouhal number difference get smaller as we move to a smaller time steps. We can conclude that time steps size of 0.1s will give us a fairly accurate representation of physical flow in term of time parameter.
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Do note that with time step size of 0.1s, we have exceeded the experimental Strouhal value of 0.183. However, we have only investigated the time parameter. We will have to investigate other parameters such as grid convergence, residual, unsteady formulation, etc, before we can conclude on the accuracy of our model. |
To determine the effect of grid convergence, a finer mesh with double the original mesh density was created. Using the time steps size of 0.1s and a refine mesh, we solved the problem in FLUENT again. With the finer mesh, we obtained Strouhal value of 0.186. As can be seen, the value is much closer to the experimental value. Further refining mesh will get us to more accurate solution.
Conclusion
For steady case, we need to check grid convergence to validate the accuracy of our result. For unsteady case, we have to validate both time parameters (time step size) and grid convergence.
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