# Incompressible BCs not fully enforced

**URL:** <https://pyfr.discourse.group/t/incompressible-bcs-not-fully-enforced/786>\
**Category:** Cases\
**Tags:** config, incompressible, bcs\
**Created:** [3 April 2023 11:42 UTC](https://pyfr.discourse.group/t/incompressible-bcs-not-fully-enforced/786 "2023-04-03T11:42:24Z")\
**Posts on this page:** 2\
**Page:** 3

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**Author:** ![WillT](https://avatars.discourse-cdn.com/v4/letter/w/bc79bd/32.png) [@WillT](https://pyfr.discourse.group/u/WillT)\
**Post date:** [25 April 2023 07:58 UTC](https://pyfr.discourse.group/t/incompressible-bcs-not-fully-enforced/786/42 "2023-04-25T07:58:08Z")

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In that figure, the wall distance is normalised by the boundary layer thickness \delta. You will need to set a thickness, unless you want \delta=1.

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**Author:** ![Yujif1Aero](https://yyz2.discourse-cdn.com/free1/user_avatar/pyfr.discourse.group/yujif1aero/32/448_2.png) [@Yujif1Aero](https://pyfr.discourse.group/u/Yujif1Aero)\
**Post date:** [25 April 2023 14:21 UTC](https://pyfr.discourse.group/t/incompressible-bcs-not-fully-enforced/786/43 "2023-04-25T14:21:24Z")

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Than you for your replying.

I may understand why the velocity of u at the wall of the inlel has not gotten zero.  
Is it ralate to the finite volume method and flux reconstruction?  
Is the value of velocity at wall extrapolated from the next poits?

I imaged the finite difference method. I am so sorry.

However, I cannot understand how to use the velocity at the wall. Could you teach me if possible?

Thank your supports so much.

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