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Fire Dynamics Simulator
https://pages.nist.gov/fds-smv/
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Relationship between DUCT_PATH and VELocity #630

Closed gforney closed 9 years ago

gforney commented 9 years ago 
Please complete the following lines...

Application Version: 5.3.0
SVN Revision Number: 3193
Compile Date: Jan. 2009
Operating System: Window XP

I simulated FDS cases to verify velocity directions when using the duct 
path. I checked the pressure trends for each case and found some 
discrepancy when referring to engineering knowledge and explanation at FDS 
user manual. The following is the summary of the case1, case3, and case4.

1. CASE-1
 o supply of air from zone 2 to zone 1 : DUCT_PATH=1,2, VEL=-2.0
 o return of air from zone 1 to zone 2 : DUCT_PATH=2,1, VEL=-3.0
 o expectation (before simulation)
   - the pressure of zone 2 will be higher than that of zone 1
   - at steady, zone 2 will be positive pressure but zone 1 to be negative.
 o simulation result
   - there is particle movement at each direction (OK!)
   - the values of pressure at zone 1 and zone 2 are same (Wrong!)

2. CASE-3
 o supply of air from zone 1 to zone 2 : DUCT_PATH=2,1, VEL=-2.0
 o return of air from zone 1 to zone 2 : DUCT_PATH=2,1, VEL=-3.0
 o expectation (before simulation)
   - the pressure of zone 2 will be increased abrouptly
   - zone 1 will show very low negative pressure (vacuum)
 o simulation result
   - the movement of particle from zone 1 to zone 2 is sparse 
(intermittent), but the flow of particle from zone 2 to zone 1 is okay.
   - the pressure of zone 2 is higher than that of zone 1 (both positive 
value)(Wrong!)

In addition, I simulated case 4 
 o supply of air from zone 2 to zone 1 : DUCT_PATH=2,1, VEL=(+)2.0
 o return of air from zone 1 to zone 2 : DUCT_PATH=2,1, VEL=-3.0
 o simulation result
   - there is particle movement at each direction (OK!)
   - the pressure value of zone 2 shows positive pressure and that of zone 
1 indicates negative pressure (my judgment : if velocity direction follows 
the conventional rule, the trend of pressure is right)

I attach case 1, case 3, and case 4 input files.

In addition, if DUCT_PATH is used to disconnected compartment, what is the 
right way to define the VEL sign (+ or - depending on its duct path)?

I guess, all these cases must be reviewed at the same time. Great thanks.

Original issue reported on code.google.com by jmhak1 on 2009-02-17 02:22:18

gforney commented 9 years ago 
Thanks. I'll take a look at these.

Original issue reported on code.google.com by mcgratta on 2009-02-17 13:07:40

gforney commented 9 years ago 
I clarified the User's Guide. It was not emphasized that you must adopt a consistent

definition of upstream and downstream based on the sign of VEL. A new Guide is 
posted.

Original issue reported on code.google.com by mcgratta on 2009-04-14 20:42:16

gforney commented 9 years ago 
Thanks for your attention.
By the way, I can not find the posted new Guide by you.
Could you show me the location to find it?

Original issue reported on code.google.com by jmhak1 on 2009-05-27 06:31:41

gforney commented 9 years ago 
Sorry -- it will come out when we release 5.4.0.

Original issue reported on code.google.com by mcgratta on 2009-05-27 11:31:53

gforney commented 9 years ago 
(No text was entered with this change)

Original issue reported on code.google.com by mcgratta on 2009-11-23 22:26:33