fds natural-gas leak

[yILCCY]

I want to simulate a case what natural gas leak by a vent. I set the model in 'Pyrosim' or 'fds code' ,The mass loss or volume flow keep same. when I change the scale of vent, suck as 0.1m x 0.1m to 0.05m x 0.05m, the velocity of gas why not increase? And Why is the leakage velocity not equal to the volumetric leakage rate divided by the leak port area .
This my question thank for answer?

[Vojta-Salek]

Hello, just to clarify: You don't see any changes in the Pyrosim interface or, for example, in the values calculated for DEVC which measures velocity in the FDS model? This is the FDS forum, so we can probably only help you with the latter. Additionally, it would be nice to provide the FDS input file that is not working correctly.

[drjfloyd]

What is your grid resolution? If your grid resolution is larger than 5 cm such that the 5 cm and 10 cm leak sizes result in the same number of grid cells being used for the VENT, then the velocity will be the same.

[yILCCY]

Thanks for you reply! In a little demo, I set the grid is 1cm x 1cm. And change the leak vent like before,but the velocity is not increase. Oppositely, it decrease

[drjfloyd]

We would need simple example input files (fds input files NOT pyrosim files) that demonstrate the problem.