MLR issue

[SaharRasoulpour]

Hello, I would appreciate your help with an issue I'm encountering. I have created a model of a wind tunnel that includes an infrared heater and some fuel particles. The infrared heater is modeled as a 9×9 cm surface maintained at a temperature of 971 K, producing a heat flux of 50 kW/m² at the surface.

The ignitor is modeled using a few non-reacting fuel particles held at a constant temperature of 1500°C, located 1.2 cm downstream of the fuel elements and centered 6 mm off the bottom. The fuel moisture content (FMC) of the vegetation is 70%.

My problem is that the total mass loss rate vs. time plot plateaus after 15 seconds. I need to determine whether this issue lies in my configuration or input file. Could you help me check if the problem is related to the ignitor?
Needle.txt

[mcgratta]

&INIT  ID='pine needles',   PART_ID='pine needles', XB=0.255,0.345,0.1,0.19,-0.005,0.0, DENSITY = 550./

This is not how one should initiate particles. DENSITY in this case refers to the density of the gas, not the particles. In the current source code, DENSITY has been removed. Read the User's Guide chapter on Particles and Droplets, specifically on insertion.

[SaharRasoulpour]

Hello, I hope you are doing well. I have a couple of questions regarding my simulation. I set the initial temperature of my ignitor to 1500°C, but when I check the ignitor, it doesn't reach the specified temperature. Additionally, the infrared fire on top of the chamber has a temperature of 971K and a heat flux of 50 kW/m², exceeding the expected values. How can I control the temperature of my ignitor and the infrared fire? It is also important to note that the ignitor's temperature should reach 1500°C to ignite and transfer the heat to the needles for pyrolysis and combustion. Moreover, when I try to use Smoke view, I can't see the temperature slice. How should I check the temperature slice in Smoke view? Your assistance would be greatly appreciated.
Wind Tunnel.txt

[mcgratta]

I suggest that you run a simple single mesh case with one pine needle. Use this case to check your model, model functionality, and if you see a potential bug, we can use this case for debugging.

[SaharRasoulpour]

If you look at the plot generated from the FDS simulation, you'll see that the temperature on the left-hand side (near the ignitor) rises and then suddenly drops to 100 degrees Celsius. I am uncertain about the cause of the temperature decrease in the bed. Could it be due to the thermal properties of the pine? I have run this case multiple times, including with a simpler setup, but the issue persists. I have uploaded the plot along with the FDS input files. Your insight and suggestions would be greatly appreciated to help me correct this and achieve accurate results.

[sample.txt](htt
vegetation_model.txt

sample.txt

[drjfloyd]

You are putting one pine needle per cell with your inputs.

[SaharRasoulpour]

Thank you for your response and consideration. I encountered an issue where, after setting N_particle_per_cell = 8, the fire propagation on the bed does not drop below 100°C after 25 seconds fortunately. The fire progresses well after that, but I’m concerned that between 50 seconds, and continuing until around 160 seconds, there’s unexpected ongoing combustion, as shown in the plot. I’ve tried adjusting the kinetic properties, but the problem persists during this interval. Do you suggest that I focus on the kinetic properties, or could this issue be related to my configuration or combustion settings?

Wind_Tunnel.txt
vegetation_model.txt

[SaharRasoulpour]

When I defined the OBST for my pine bed, that region improved, but the peak temperature increased significantly. If I want to control the peak temperature—reducing it from 800°C to 600°C—which parameter should I focus on? Is it correct to define OBST for my pine bed? I added OBST because some FDS samples included OBST in the pine bed. My plots are close to what I want, but I still have some issues. In my last message, my sample didn’t have OBST for the pine bed, but in this case, it does.
!PINE BED:
&SURF ID = 'Pine Needles'
MATL_ID = 'GENERIC VEGETATION'
MOISTURE_FRACTION = 0.7
SURFACE_VOLUME_RATIO = 8366.
LENGTH = 0.09
GEOMETRY = 'CYLINDRICAL' /

&PART ID = 'Needles'
DRAG_COEFFICIENT =0.375
COLOR = 'GREEN'
SURF_ID = 'Pine Needles'
QUANTITIES = 'PARTICLE TEMPERATURE','PARTICLE MASS'
STATIC = .TRUE.
EMBER_PARTICLE = T
EMBER_DENSITY_THRESHOLD = 70.
EMBER_VELOCITY_THRESHOLD = 0.
TRACK_EMBERS = F /

&INIT PART_ID = 'Needles'
XB = 0.255,0.345,0.085,0.175,0,0.005
N_PARTICLES_PER_CELL = 8
CELL_CENTERED = .TRUE.
DRY = T /
&OBST XB=0.255,0.345,0.085,0.175,0,0.005, COLOR='WHITE', TRANSPARENCY=0.5 , SURF_ID='Pine Needles', BULK_DENSITY=42.9 /