Surface pressure values seem to be incorrect?

grasshopper butterfly
1

Dear community,

I am running an outdoor airflow simulation with butterfly, and the results I am getting for the surface pressures seem to be incorrect. Any help is appreciated!

Below I will post 2 cases and elaborate on them. For clarification, I am visualizing the pressures as vectors to make it easier to see if they are positive or negative (positive will point inwards, and negative will point outwards). In both cases, the wind speed is 30 m/s and orthogonal to the front side of the butterfly geometry.

Case 1
The simulation is performed on a cube with 10 m sides. Here are the results:

top2
top2708×626 35.3 KB

Here, the pressures on the windward side seem to be okay, but on the sides and the leeward end I am getting positive pressures. These should be negative, right?

Here are more pictures of the colored mesh faces:

front 2
front 2783×629 70.1 KB

Front

back2
back2789×617 66.2 KB

Back

press2
Pressure Values

This is the solution log: simpleFoam.log (421.8 KB)

Case 2
Here, the simulation is run with the same parameters, but on an extruded surface with thickness of 5 m.
Top
Here the vectors point as they should (positive on windward side, and negative on all other sides)

Further pictures:
Front
Front

Back
Back744×455 46.5 KB

Back

Press
Press454×583 17.4 KB

Pressure Values

Does anyone have an idea why this is happening? I can provide more files if they would help in resolving the issue.

Thanks in advance!

2

Possible answer:

OpenFoam pressure probes are showing the static pressure at the sampled point. To get the actual pressure acting on the surface one would need to calculate DeltaP = Pref of the freestream - Pstat at the probe point.

3

I have never checked the surface pressure on garasshopper before.
Have you tried checking the results in Paraview?
Is the velocity field as expected?

4

The results seem to be okay in Paraview. I will dig deeper and post any updates here

5

Hi, I have the same problem when I am doing the outdoor airflow simulation. The wind pressure on the side surface of the building shows positive to me. May I ask if you have found the way to solve it?