Large errors in FM/FPRF Datacenter

[mcgratta]

These two plots of smoke concentration

show significant error in the red points. Could you double check these runs. If it is what it is, just leave it. But double check to see that there is not something obviously different between the set ups of model and experiment.

[drjfloyd]

At first glance these two input files are the same as the C3H6_SF files except for the burner location (HA is burner in hot aisle and SF is burner in subfloor). I ran one for T_END=0 and the geometry and instrumentation locations look OK. I'll need to take a deeper look to make sure I am not missing something.

[drjfloyd]

I think this is just what it is. The ceiling of the hot aisle has drop ceiling with a checkerboard pattern of perforated metal mesh grates.

In FDS these are being modeled with particles with the drag tuned to get manufacturer reported pressure drops. In the FDS case, smoke from the fire is moving straight up and through the openings in the ceiling. It is probably that in reality the grates result in a small amount of smoke moving along the ceiling to the next set of openings where the HA (hot aisle) measurement point being compared to is.

Reading the reports for this work again reminded me that this used a ring burner. When I set these cases up a decade ago I did them with a typical solid block burner. I can try with a case where I use particles to make a ring like we do for the douglas fir case to see if that causes any changes in the smoke plume that result in a little more smoke at the room center.

[mcgratta]

Could those vents be modeled as HVAC localized leakage vents? Such that the higher pressure below the ceiling might push most, but not all, of the smoke upwards?

[drjfloyd]

They are 2 x 2 vents. Localized leakage would impose a constant velockity over them. Back when I was setting these up that caused more issues that it fixed. Possible various bug and other changes since has changed that.

[drjfloyd]

I tried with localized leakage at the ceiling tiles
I tried with localized leakage at the ceiling tiles and limiting cross flow at the entrance/exits of the racks (like done with the subfloor).
I tried the current particles in the ceiling tiles with limiting cross flow in the racks and at the ceiling.

Minor shifts in results with each. A little better here a little worse there, but nothing that is significantly different than the current results.