how to start fire at a time different from 0?

[Mohammad Tavakol]

Hello everyone. 
I am trying to simulate some field-scale grassland fires but the problem is that the fire starts exactly when the simulation is started and does not let the wind fully develop. So, i would be very thankful if you could help me how to solve this issue. how to start the fire at a desired time? 

I am using vents to start the ignition. 

Thank you

[Kevin McGrattan]

Use a RAMP. More in the FDS User Guide.

[Dave Sheppard]

If you want to start a model where there is an existing velocity field, try using a UVWFILE. This functionality is described in the 'Velocity Field' section of the user's guide.

To use this functionality you run a model (with or without a fire) and have the model develop its initial velocity field.  The velocity field in the domain can be saved in a UVWFile.

Then in subsequent models the UVWFile from the first run is used to define the initial velocity field at the start of the model runs.

[Mohammad Tavakol]

Thanks every body. that was really helpful.