# Normal condition at wall

**URL:** <https://community.freefem.org/t/normal-condition-at-wall/1442>\
**Category:** General Discussion\
**Created:** [January 17, 2022, 2:58pm UTC](https://community.freefem.org/t/normal-condition-at-wall/1442 "2022-01-17T14:58:01Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![zese](https://yyz2.discourse-cdn.com/flex030/user_avatar/community.freefem.org/zese/32/917_2.png) [@zese](https://community.freefem.org/u/zese)\
**Post date:** [January 17, 2022, 2:58pm UTC](https://community.freefem.org/t/normal-condition-at-wall/1442/1 "2022-01-17T14:58:01Z")

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Dear all

I have a problem in defining my boundary condition.  
I have to define a jet on a wall (1) whose direction is normal to the wall and I just have the abs value of the jet so Vj= Aj\*(N.x+N.y) ? Aj is the magnitude. now how I can define it to solve the equation?  
on(1,ux=Aj_N.x,uy=Aj_N.y)?!

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<div class="post-metadata">

**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:** [January 31, 2022, 4:19pm UTC](https://community.freefem.org/t/normal-condition-at-wall/1442/2 "2022-01-31T16:19:57Z")

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yes , but warning its this you jet is not like a Poisseuille flow because you normal is given by A  
of coarse A could be a function of (x,y)…

`on(1,ux= N.x*A,uy=Ny*A),`