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Old   April 28, 2016, 07:26
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MANI VINAYAK
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Hii.. i am new to CFD. I am doing spanwise lift analysis for my wing design.i have no idea how to do grid independence test for my model.please help me with it.
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Old   April 28, 2016, 10:27
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Alex Pasic
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Just start with a coarse grid (let's say 50 points spanwise) and refine the mesh in all directions (both normal to the wing and spanwise/chordwise) until results stop differing between the solutions (or at least differ <2%). Then you can call your solution grid independent.
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Old   April 28, 2016, 10:38
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okay...but what u mean by solution? the Cl values which i want to get from cfd post?
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Old   April 28, 2016, 10:48
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Yes. Any observable value or whatever you're aiming to present. You can also set up a Cl, Cd, Cm or other monitor in FLUENT (no need to wait until it's all over to get to CFD-Post). So, let's say you're trying to match the results of an experiment and those are Cd=0.15 and Cl=0.5 or whatever.

Your first (coarse/rough) grid gives you Cd=0.19 and Cl=0.33, then you refine your grid and run the simulation again, this time Cd=0.17 and Cl=0.42. Next refinement step Cd=0.157 maybe and Cl=0.485.. and last refinement you get to 0.152 and 0.496.

The percentile change between the last two Cd results is ~3% and for Cl it's ~2,3%. You might as well call this grid independent or do another refinement and run again. It's just important to show that you are asymptotically approaching a single value (this can be an experimental value or an analytical solution) - at least until things like round off errors and discretisation errors come into play.
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Old   April 28, 2016, 10:54
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oh okay..thank you so much..that was very helpful sir
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