# On grid independent solution for pulsatile flow

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 June 7, 2005, 14:01 On grid independent solution for pulsatile flow #1 David Guest   Posts: n/a Hi all, I am modelling a 2d pulsatile flow in a conical tube for an undergraduate project. This tube is about 15 cm long with a radius varying between 6.5 mm and 12.5 mm. I use a velocity inlet and a pressure outlet. I am trying to acheive an grid independent solution. To do so, I compare a grid having 200 000 cells vs. one having 800 000 cells. I have set-up monitors for various quantities including the area-weighted velocity magnitude of points lying on the centerline (symmetry axis) of the tube. When comparing the 2 cases I get satisfying results. My problem is when monitoring the integral of wall shear stress on the wall of the tube. I get vary different values (30% error) when taking the cycle time-average. My question is does this mean that my grid is not fine enough? Can someone give an order of magnitude as to how many cells I should be using to obtain a grid-independent solution? From what I had read I tought 200 000 cells would be more than enough for a laminar case... Any comments would be much appreciated. Thanking you in advance for your time. David

 June 8, 2005, 09:54 Re: On grid independent solution for pulsatile flo #3 David Guest   Posts: n/a Hi Aaron, Thank you so much for your comments. They really give me a good explanation. One other question: At some point you mention :"Don't make any changes to the grids (other than grid size)[...]". Does that mean that grid adaption should be avoided. In my case I used it because some of the cells near the wall did not have a good aspect ratio near the wall (both for the 200k and 800k grids). Is this a potential source of more trouble that need to be? Best Regards, David

 June 8, 2005, 16:20 Re: On grid independent solution for pulsatile flo #5 David Guest   Posts: n/a Many thanks Aaron, Your comments are very much appreciated! Best Regards, David

March 25, 2022, 03:33
Difficulty in obtaining grid independent value
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Vidya Muthulakshmi M
Join Date: Aug 2020
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Hi,

Very useful reply. But I am getting increased error with increased mesh density. Can someone let me know what can be the reason?