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Fire Dynamics Simulator
https://pages.nist.gov/fds-smv/
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Pressure loss computation #1649

Closed gforney closed 9 years ago

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

Application Version: 5.5.3 Serial
SVN Revision Number: 7031
Compile Date: 29 October 2010
Operating System: Windows 64

Describe details of the issue below:

I am attempting to use FDS to compute pressure loss through a tunnel without and with
a fire. Two files are attached:

tvB-07-01 - No fire case, smooth walls, 4m wide by 5m high, 250m long, inlet velocity
3m/s (generated by applying a mass flux at the end of the domain and an open boundary
+ restriction at the inlet - this is done to trigger a fluctuating velocity field).
This model gives a good prediction of the pressure loss (i.e. only loss is due to wall
friction and when I compute wall friction using the Moody diagram and compare with
the FDS pressure losses, computed from H, the comparison is very good).

tvB-07-02 - This is the same case as tvB-07-01 but now there is fire 150m into the
domain. The pressure loss upstream is very large. I would have expected it to be the
same as a no fire cases upstream but this is not the case. Downstream I get a reasonable
pressure change.

I have tried a few different combinations of inlet/exit boundary conditions, including
a velocity inlet and open exit. I have also tried adjusting some solver parameters
such as the baroclinic parameter, and I have also made the velocity tolerance and number
of iterations more onerous for the pressure solver.

Original issue reported on code.google.com by matt.bilson76 on 2012-07-22 13:31:38

gforney commented 9 years ago 
Please provide a simple write up of this case to demonstrate what the analytical solution
ought to be.

Original issue reported on code.google.com by mcgratta on 2012-07-23 12:20:45

gforney commented 9 years ago 
Please see attached PDF document and zip file with the devc files and my post processing
calculations.

Original issue reported on code.google.com by matt.bilson76 on 2012-07-23 15:21:07

gforney commented 9 years ago 
I don't see where 5 MW is entering these calculations. Wouldn't we expect the thermal
expansion of the fire to have a significant effect on the tunnel pressures?

Original issue reported on code.google.com by mcgratta on 2012-07-23 16:16:22

gforney commented 9 years ago 
I have not undertaken a calculation for the pressure loss due to a 5 MW fire. To my
knowledge there is not a reliable method available to do this. In previous designs
we have relied on heuristics for this element, or sometimes CFD. I agree the thermal
expansion will have an effect. The attached gives a little more explanation of what
I expected to see for the 5 MW fire and what I actually saw.

Original issue reported on code.google.com by matt.bilson76 on 2012-07-23 20:32:41

gforney commented 9 years ago 
I ran the tvB-07-02.fds case, and everything appears to be working properly. I do not
know off the top of my head what sorts of pressure drops to expect, but I've no clear
indication that something is wrong.

Original issue reported on code.google.com by mcgratta on 2012-07-23 20:57:11