# how to do a grid independent study

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 November 9, 2010, 11:05 how to do a grid independent study #1 Member   newansysuser Join Date: Oct 2010 Posts: 33 Rep Power: 7 Hello everyone I want to do a grid independent study on my model, the model is only 5mm width, 2D I add inflation layer on the wall and set the element size in the middle. what kind of critiria is for the grid independent? After a coarse mesh, decrease the inflation layer and element size by the same ratio? And for my pc , it can't stand the cell size smaller than 0.08mm. Can I finish the grid independent study on this model?

 November 9, 2010, 11:07 #2 Member   newansysuser Join Date: Oct 2010 Posts: 33 Rep Power: 7 I have read all the threads about grid independent in this forums, and I also asked my instructors, he has no idea, so please tell me if you know , thank you in advanced.

 November 15, 2010, 12:28 #3 Senior Member   Join Date: Feb 2010 Posts: 145 Rep Power: 9 Systematically decrease the element size by half and quantify the error, such as the maximum value of the streamfunction. For example, suppose there are two regions in the flow, namely, the bulk of the flow and the boundary layer. Start with the default mesh. In the bulk of the flow, decrease the element size and quantify the error. Repeat until the error is within tolerance. In the boundary layer, repeat the same procedure. That is, keep decreasing the mesh until the solution is independent of the grid. Good luck! rgd and engineer.iman like this.

February 6, 2011, 18:27
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John
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Quote:
 Originally Posted by Jade M Systematically decrease the element size by half and quantify the error, such as the maximum value of the streamfunction. For example, suppose there are two regions in the flow, namely, the bulk of the flow and the boundary layer. Start with the default mesh. In the bulk of the flow, decrease the element size and quantify the error. Repeat until the error is within tolerance. In the boundary layer, repeat the same procedure. That is, keep decreasing the mesh until the solution is independent of the grid. Good luck!
how to know that the solution is independent of the grid?

 February 8, 2011, 07:19 #5 New Member   zhao xin Join Date: Feb 2010 Location: Goteborg Posts: 28 Rep Power: 8 Untill your result comes to the value within an acceptable error compared to the last one. engineer.iman likes this.

 December 24, 2013, 07:47 #6 Member   Join Date: Dec 2013 Posts: 53 Rep Power: 4 Hi I have simulated flow over solids.I have applied periodic boundary conditions in GAMBIT.I have run the case in FLUENT and the case got converged.After I change the grid size to finest and most coarser, the values far away from the converged case ,I see the same results .Why is this happening?

 January 22, 2014, 01:13 #7 New Member   Join Date: May 2013 Posts: 4 Rep Power: 5 What tolerance are you setting for your convergance criteria. Increase it a little bit, say 10e-5 and then see your results.

 July 13, 2016, 12:53 Grid Independence Study #8 New Member   KARNATAKA Join Date: Jul 2016 Posts: 1 Rep Power: 0 In ANSYS CFX i am performing thermal analysis of motor. I have done meshing for the motor in HYPERMESH tool and exported file to ANSYS CFX. I have selected the element length size of 5 mm and i got around 3.5 million elements.After initializing domain interfaces, boundary conditions i have run the simulation and got the results. In order to verify the results, again in HYPERMESH for the same meshed model i just increased the number of elements by re-meshing the model. Again in CFX after simulation i am getting the same results. The result won't vary what i got from the previous meshed model. Does this mean i have reached mesh independence study and got the expected results? Please give me your feedback, I am new to CFD. Since i am from the electrical background i don't have much idea about the mesh independence study.

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