Re: [fds-smv] Angled/Louver Vent with Volume_Flow

[Kevin McGrattan]

You can use VOLUME_FLOW and VEL_T together. The first defines the normal component of velocity; the second the tangential. 

[Richard]

Richard

8:06 PM (now) 

to FDS and Smokeview Discussions

So to clarify.  And to make things absoutely as simple as possible so I can understand these parameters.
VOLUME_FLOW = 1m3/s. 
Temperature = 13C.

So the simple surface would be:
&SURF ID = 'Supply' TMP_FRONT=13 VOLUME_FLOW=-1/

But that 1m3/s is obviously not velocity right?
So I need to divide my flow rate by the area of my vent to get Velocity, then using Pythagoras to get the normal velocity tangential velocity.  And since it's 45 degrees the two component will be the same.
And to keep thing simple, If my vent area = 1m2 then:

V^2  = Vn^2 + Vt^2
Vn = Vt bc 45 degrees then V^2 = 2Vn^2 = 1^2 = 2Vn^2 = 1 = 2Vn^2
Vn^2 = 1/2 = 0.5
Vn = sqrt(0.5)
= 0.707107

So:
&SURF ID = 'Supply' TMP_FRONT=14 VEL=- 0.707107 VEL_T= - 0.707107 /

OR could it be:
&SURF ID = 'Supply' TMP_FRONT=14 VOLUME_FLOW=-1 VEL_T= -0.707107 /

[dr_jfloyd]

It is only the normal component of velocity that adds mass to the room. If you want 1 m3/s into the room, then both components would be 1 m/s.

[Richard]

I'm sorry this is too confusing.
If I want the final result to be 1m3/s angled 45 degrees down into the room (Red).  My normal component (Yellow) and tangential component (Blue) should be 0.707 no?


If I'm not even grasping the concept of vector correctly and it is 1m/s then should the parameter be
&SURF ID = 'Supply' TMP_FRONT=14 VEL=- 1 VEL_T= -1 /
Or
&SURF ID = 'Supply' TMP_FRONT=14 VOLUME_FLOW=-1 VEL_T= -1 /

[dr_jfloyd]

Only the normal vector component adds mass to domain. The parallel component just takes the mass that is already in the domain and push it in the direction of that component. If you have a 1 m2 vent and want 1 m3/s to be added to the domain, you need to have the normal component be 1 m/s.

[Richard]

Okay in that case is it:

&SURF ID = 'Supply' TMP_FRONT=14 VEL=- 1 VEL_T= -1 /
Or
&SURF ID = 'Supply' TMP_FRONT=14 VOLUME_FLOW=-1 VEL_T= -1 /

[dr_jfloyd]

If your VENT is 1 m^2 then the two inputs are equivalent. In the second line FDS will compute VEL = VOLUME_FLOW / Vent Area

[Mateusz Fliszkiewicz]

Maybe someone will find it useful:

https://docs.google.com/spreadsheets/d/1g104-aAPS2IBXcMAGJbSJw58uQQh0pV9JhPTTdyay44/edit?usp=sharing