jet fan

[baran khaksari]

Hi Friends,

I try to simulate a jet fan. Although I define OBST,  FDS simulation shows the below error:

VENT 9 must be attached to a solid obstruction.

&MESH ID='MESH01',IJK=100,180,120, XB=-2.0,1102,-13.0,2.53,-1.0,7.0/

#FAN 9&10

&OBST XB= 160.0,163.0,-6.35,-5.35,4.33,5.33, COLOR='RED' /

&VENT XB= 160.0,160.0,-6.35,-5.35,4.33,5.33 ,SURF_ID='HVAC',ID='IN_3',COLOR='RED'/

&VENT XB= 163.0,163.0,-6.35,-5.35,4.33,5.33,SURF_ID='HVAC',ID='OUT_3',UVW= -1,0,0,COLOR='RED'/

&HVAC ID='IN_3',TYPE_ID='NODE',DUCT_ID='JET FAN_3',VENT_ID='IN_3'/

&HVAC ID='OUT_3',TYPE_ID='NODE',DUCT_ID='JET FAN_3',VENT_ID='OUT_3'/

&HVAC ID='JET FAN_3',TYPE_ID='DUCT', NODE_ID='IN_3','OUT_3',VOLUME_FLOW=3,AREA=1.0,RAMP_ID='JET'/

By the way, I want to simulate the tunnel ventilation airflows increase linearly up to 3 m/s over a period of approximately 5 minutes. Therefore, I determine the below RAMP. If I RAMP_ID in HVAC, does it work?

&RAMP ID='JET', T=0, F=0/

&RAMP ID='JET', T=30, F=0.1/

&RAMP ID='JET', T=60, F=0.2/

&RAMP ID='JET', T=90, F=0.3/

&RAMP ID='JET', T=120, F=0.4/

&RAMP ID='JET', T=150, F=0.5/

&RAMP ID='JET', T=180, F=0.6/

&RAMP ID='JET', T=210, F=0.7/

&RAMP ID='JET', T=240, F=0.8/

&RAMP ID='JET', T=270, F=0.9/

&RAMP ID='JET', T=300, F=1/

Would you please guide me.

Baran

[Randy McDermott]

First, the error message is pretty clear.  I would open the model in Smokeview and toggle "q", which shows the input geometry compared to the grid-snapped geometry.  If your VENT ends up away from the final geometry, this will cause a problem.

Second, if you are going to ramp something linearly, just use two points.  Simplify.  That's probably not the root cause of the HVAC problem, but it speaks to how you may be over complicating things.  Start from a very simple input file.  Build it gradually and run short test cases along the way.  Then you will know immediately what causes a problem.

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[baran khaksari]

Dear Randy,

Thank you for your reply but I have another jet fan in a different longitudinal location which does not show any problem.

#JET FAN 1&2

&OBST XB= 80.0,83.0,-6.35,-5.35,4.33,5.33, COLOR='RED' /

&VENT XB= 80.0,80.0,-6.35,-5.35,4.33,5.33 ,SURF_ID='HVAC',ID='IN_1',COLOR='RED'/

&VENT XB= 83.0,83.0,-6.35,-5.35,4.33,5.33,SURF_ID='HVAC',ID='OUT_1',UVW= -1,0,0,COLOR='RED'/

&HVAC ID='IN_1',TYPE_ID='NODE',DUCT_ID='JET FAN_1',VENT_ID='IN_1'/

&HVAC ID='OUT_1',TYPE_ID='NODE',DUCT_ID='JET FAN_1',VENT_ID='OUT_1'/

&HVAC ID='JET FAN_1',TYPE_ID='DUCT', NODE_ID='IN_1','OUT_1',VOLUME_FLOW=3,AREA=1.0,RAMP_ID='JET'/

Regards,

Baran

[Baran Khaksari]

Hi Friends,

Would you please somebody guide me.

The simulation is for a 1.1 km tunnel with 26 jet fans along the tunnel. I attached the FDS file also.

Regards,

Baran

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[Mateusz Fliszkiewicz]

Hi Baran,

if you have problem with defining jetfan you can use this link: https://wizfds.com/login?demo=true Jetfans are implemented in wizfds and you will get fds output for your boundary conditions. Screenshot below:

[dr_jfloyd]

Your grid size is 11 m x 0.09 m x 0.07 m.  You should read the FDS User Guide discussion on grid aspect ratio.

Your jet fan OBST are 3 m x 1 m x 1m and you are putting the vents on the x faces.

You need to look at your geometry in Smokeview and see what happens when you try and place a 3 m OBST into an 11 m grid.