# The equations in the "large fluid simulation" is wrong

**URL:** <https://community.freefem.org/t/the-equations-in-the-large-fluid-simulation-is-wrong/2275>\
**Category:** General Discussion\
**Created:** [February 11, 2023, 1:23am UTC](https://community.freefem.org/t/the-equations-in-the-large-fluid-simulation-is-wrong/2275 "2023-02-11T01:23:37Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![cfdyuewu](https://avatars.discourse-cdn.com/v4/letter/c/5f8ce5/32.png) [@cfdyuewu](https://community.freefem.org/u/cfdyuewu)\
**Post date:** [February 11, 2023, 1:23am UTC](https://community.freefem.org/t/the-equations-in-the-large-fluid-simulation-is-wrong/2275/1 "2023-02-11T01:23:37Z")

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[https://doc.freefem.org/tutorials/aLargeFluidProblem.html](https://doc.freefem.org/tutorials/aLargeFluidProblem.html)  
the navier-stokes is wrong, the correct form is  
 ![image](https://canada1.discourse-cdn.com/flex030/uploads/freefem/original/2X/6/6e0a394b5023beadf6556a29d885a1847268bf00.png)  
the divergence of the product of miu\_{T} and the transpose of grad(u) is missing, it can’t be eliminated because miu\_{T} is not constant

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**Author:** ![frederichecht](https://yyz2.discourse-cdn.com/flex030/user_avatar/community.freefem.org/frederichecht/32/15_2.png) [@frederichecht](https://community.freefem.org/u/frederichecht)\
**Post date:** [February 11, 2023, 5:33pm UTC](https://community.freefem.org/t/the-equations-in-the-large-fluid-simulation-is-wrong/2275/3 "2023-02-11T17:33:33Z")

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It is a well know simplication un case of Boussinesq approximation for the buoyancy, and the resultat are on golf agreement with experiment.