Wind velocity is not right at reference elevation

[mcgratta]

In this case, the specified wind speed is not achieved at the reference elevation

&HEAD CHID='Case_6_new' TITLE='Description of flt1fuel1mps' /

&TIME T_END=360. /

&MULT ID='Meshes' DX=200. I_UPPER=3 DY=200 J_UPPER=3 /
&MESH IJK=50,50,50 MULT_ID='Meshes' XB=-400.,-200.,-400.,-200.,0.00,200. /

&VENT MB='XMIN' SURF_ID='OPEN' /
&VENT MB='XMAX' SURF_ID='OPEN' /
&VENT MB='YMIN' SURF_ID='OPEN' /
&VENT MB='YMAX' SURF_ID='OPEN' /
&VENT MB='ZMAX' SURF_ID='OPEN' /

&DEVC ID='u', XB=10,10,10,10,1,199, POINTS=50 QUANTITY='U-VELOCITY' /
&DEVC ID='T', XB=10,10,10,10,1,199, POINTS=50 QUANTITY='TEMPERATURE' /

&SLCF PBY=0.00 QUANTITY='VELOCITY' /
&SLCF PBY=0.00 QUANTITY='TEMPERATURE' VECTOR=T /

&WIND SPEED=1., DIRECTION=270, L=-100., Z_0=0.03, Z_REF=20 /

&TAIL /

[mcgratta]

[mcgratta]

The reference temperature and velocity were not exactly achieved at the reference elevation. They should now be.

[mcgratta]

You can download a test version of FDS that fixes the issue of reference velocity, temperature and height. Check that things work and then we can address other issues if they still exist.

[shahabck3]

Thanks, Kevin, I will give it a go!

[mcgratta]

Did this fix the problem?

[shahabck3]

I did not have a chance to try it yet, I was running other tasks.

I will work on it this week and let you know.

Thanks

[mcgratta]

Thanks for checking.

[shahabck3]

Dear Kevin, I have to say that I don't know how, but still I get incorrect results in some cases.

I ran two cases with a stable stratification, and the wind readings were lower than specified at the reference height.

[mcgratta]

Are you saying you don't know how to install a nightly build? The nightly builds are here.

[shahabck3]

No, I'm saying that I ran some tests with the nightly build, but the windspeed was lower than specified at reference elevation.

[mcgratta]

Could you post a case that has a lower than specified wind speed.

[shahabck3]

Sure, here is the case for 2m/s wind @ 6m reference height. But the readings at 6m is around 1.6m/s flt1fuel2mps_line.csv [flt1fuel2mps.txt](https://github.com/firemodels/fds/files/13952608/flt1fuel2mps.txt)

[mcgratta]

You need to establish the GROUND_LEVEL on the WIND line.

[mcgratta]

It is difficult to debug your case because the vertical grid resolution is 2 m. Look at this case

&HEAD CHID='wind' /
&TIME T_END=300. /
&MESH IJK=100,100,20, XB=-50.,50.,-50.,50.,1.,21. /
&VENT DB='XMIN' SURF_ID='OPEN' /
&VENT DB='XMAX' SURF_ID='OPEN' /
&VENT DB='YMIN' SURF_ID='OPEN' /
&VENT DB='YMAX' SURF_ID='OPEN' /
&VENT DB='ZMAX' SURF_ID='OPEN' /
&DEVC ID='u', XB=0,0,0,0,1.5,20.5, POINTS=20, QUANTITY='U-VELOCITY' /
&SLCF PBY=0.00 QUANTITY='TEMPERATURE' VECTOR=T /
&WIND SPEED=2., DIRECTION=270., L=1000000 , Z_0=0.03, Z_REF= 6, GROUND_LEVEL=1 /
&TAIL /

[mcgratta]

Anything further on this issue? Are you still having trouble?

[shahabck3]

I am running a simulation with a smaller mesh size, but it's taking a bit of time. I will let you know as soon as it finishes.

[mcgratta]

I'm going to close the issue. Start a new issue if there are still problems, or reopen this one.