# CFD of an UAM

**URL:** <https://www.simscale.com/forum/t/cfd-of-an-uam/97187>\
**Category:** CAD & Meshing\
**Created:** [June 9, 2023, 4:10am UTC](https://www.simscale.com/forum/t/cfd-of-an-uam/97187 "2023-06-09T04:10:42Z")\
**Posts on this page:** 1\
**Showing post:** 2

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**Author:** ![kaany](https://www.simscale.com/forum/user_avatar/www.simscale.com/kaany/32/57613_2.png) [@kaany](https://www.simscale.com/forum/u/kaany)\
**Post date:** [June 9, 2023, 7:59am UTC](https://www.simscale.com/forum/t/cfd-of-an-uam/97187/2 "2023-06-09T07:59:15Z")

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Hello, and thank you for using the Forum!

A few points I’d like to address are:

1. Symmetry faces on the top and bottom faces of the external flow domain: While it’s not technically incorrect to apply symmetry faces there, it is more commonly recommended to define slip walls.

2. Pressure input in [Pressure Outlet](https://www.simscale.com/docs/simulation-setup/boundary-conditions/pressure-inlet-and-pressure-outlet/#pressure-outlet) boundary condition for incompressible flows: In the case of incompressible flows, the pressure input in the Pressure Outlet boundary condition is typically specified as gauge pressure. The general approach is to use a reference pressure of 0 Pa (gauge pressure). This means that the pressure value you input is relative to the reference pressure.

3. y+ value and wall resolution: When manually defining the inflation layers, it is crucial to [ensure that the y+ values fall within an appropriate range](https://www.simscale.com/forum/t/what-is-y-yplus/82394). For wall functions, a common guideline is to maintain a range of 30 \< y+ \< 300, while for the full resolution approach, y+ should be less than or equal to 1. In the current case, it seems that there are regions on the VTOL with y+ values exceeding 1000, indicating that the wall cannot be properly resolved. This can lead to inaccuracies in the flow simulation and should be addressed by adjusting the mesh and/or refining the inflation layers.

I hope these would be helpful,  
Kaan

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