Unsteady Results-Flow over a sphere
Hi everyone,
i have a question about my unsteady cfd results. I am simulating a time-dependent (unsteady at inlet velocity 20 m/s) flow over a sphere with Star CCM+ which is in the middle of the wind tunnel. Also some pictures are saved in every time-step. After some time-steps I mean the time= about 0.5 s, the velocity and also vorticity distributions change really minimally, as opposed to the time between 0-0.5s. So that i cant see the turbulent structures on these distributions. The solution is like an end result of a steady state! (Time-Step is chosen= 0.002s) I have expected that the periodic fluctating behaviour could be clearly seen. Is it normal that the flow can be stable in this case? Or is it unrealistic how I define the problem? :confused: Thanks in advance. |
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What about the diameter and the fluid? What about the details of your numerical formulation? |
Sorry for the missing informations about my model. It is an air flow over a sphere with 220 mm diameter like a soccer ball. The mesh size in the wake is 6 mm.
I think it is a general question for me, because the same thing occured when i tried to simulate a vehicle aerodynamic problem in transient case. I observed, it doesnt come to almost no changes when i looked at velocity distributions after certain time-steps. So, could it be a problem at the my problem definition or is the time step i have chosen a wrong value? Or Do I have to make the mesh size finer in the wake? Thanks |
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No, the first and more relevant think is about the mathematical set of equations you are solving. What kind of formulation are you using? Be aware that your Re is O(10^5). This is a very critical regime, see https://www.grc.nasa.gov/www/k-12/ai...ragsphere.html This flow is very challenging, requires a proper formulation and a very refined grid |
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