Question about Localized Leakage vent surface setting

[Jack]

Dear all,

I want to run simulation using localized leakage. According to FDS User Guide (version6.6.0, p.119-120), two vents should be set as the leakage path. The guide says that the SURF_ID for VENT with localized leakage is not 'HVAC' but does not point out which type of surface the vent should be. The input line example defines two different SURF_ID of two vents.

Q1: What kind of SURF_ID should be for vents used in localized leakage?

Q2: Should the SURF_ID of different vents be different? Can I define two vents with the same SURF_ID?

Thanks in advance!

Regards,

Jack

[dr_jfloyd]

The SURF_ID on each side should reflect that of the surface that is leaking.  For example, if your leak path were a crack around a door, you would want to assign the same SURF_ID as you used for the rest of the door. Any SURF_ID, as long as it doesn't specify a flow (for example VEL, MASSFLUX, or a pyrolysis model), can be used for either side of the leak path.

[Salah Benkorichi]

See the examples in the HVAC folder

leak_test*

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[Jack]

Hi dr_jfloyd,

Thanks for your reply. Your reply has answered my questions. But I have one doubt: if there is a crack around a door, it should be a hole in reality. Is it appropriate to assign the same SURF_ID between the leak and door?

Regards,

Jack

在 2018年3月9日星期五 UTC+1下午5:41:50，dr_jfloyd写道：

[Jack]

Hi Salah,

Thank you for your reply. The leak_test example in HVAC folder uses pressure zone (bulk) leakage method rather than localized leakage method. I don't find examples using localized leakage method in the folder. But the previous reply made by dr_jfloyd has answered my questions.

Regards,

Jack

在 2018年3月9日星期五 UTC+1下午5:44:22，Salah Benkorichi写道：

See the examples in the HVAC folder

leak_test*

On 9 March 2018 at 16:34, Jack <junyi...@gmail.com> wrote:

Dear all,

I want to run simulation using localized leakage. According to FDS User Guide (version6.6.0, p.119-120), two vents should be set as the leakage path. The guide says that the SURF_ID for VENT with localized leakage is not 'HVAC' but does not point out which type of surface the vent should be. The input line example defines two different SURF_ID of two vents.

Q1: What kind of SURF_ID should be for vents used in localized leakage?

Q2: Should the SURF_ID of different vents be different? Can I define two vents with the same SURF_ID?

Thanks in advance!

Regards,

Jack

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[dr_jfloyd]

Localized leakage is to allow you to represent the flow through openings that are too small to resolve on the current grid.  In general this means that the VENT area the leak is being applied to is predominately something other than the leak.  Consider a typical interior door which might have a gap of a few mm at its bottom.  Odds are in an FDS model you would have grid cells that are multiple cm in size.  A few mm gap in a grid cell that is multiple cm is a small fraction of the area of the cell. At that point most of the wall cell for the VENT is actually the door and the error in assuming it is all door would be small.  

[Jack]

Dear Jason,

Thank you very much for your detailed explanation! I understand it now.

Regards,

Jack

在 2018年3月9日星期五 UTC+1下午6:43:46，dr_jfloyd写道：

[TimoK]

Well, why you do need the SURF_ID for a localized leak VENT? As Jason said, most of the VENT is actually not a "vent", but a real surface like the wood on the door. So, you need SURF_ID so that FDS can compute the heat transfer to the real solid OBST at the "localized vent location". But, as Jason said, be careful: You can not have "velocity boundary condition" here, e.g., this part of your wooden door can not "burn" (= have a pyrolysis reaction defined or a HRRPUA or anything similar).

TimoK

[Jack]

Hi TimoK,

Thank you for your reply. I will be careful in the simulation.

Jack

在 2018年3月12日星期一 UTC+1上午9:04:17，TimoK写道：