[Jayhawk]

I am trying to model a pressure safety valve's (550 psig) exhaust stream (natural gas) into the ambient air (14.7 psia) around it. The valve is connected to a natural gas pipeline so I have that continnum and also the air continuum around it. (As well as the piping continuum.)

I have a few questions on how to best carry this out:
1. First a dumb question. It's not as though I have to worry about the simulation modeling the pipe interior as becoming a vacuum once its initial volume of natural gas is exhausted, right? I assume I don't need to model in a larger volume for the natural gas to be coming from. (My inlet is modeled as a stagnation inlet at 550 psig, and the outlets are pressure outlets at ambient pressure.)

2. I found this thread which was somewhat relevant: http://www.cfd-online.com/Forums/sta...-continua.html ,to achieve this natural gas flow going into ambient air do I need to set up a multiphase simulation? None of the tutorial examples seem to cover this. When I try to set-up the interfaces now and I have the regions with different physics continua, I can only have a baffle interface between them which of course won't work.

3. For my "Air/Gas Inlet" interface I have unchecked the "Enable" option as those two areas aren't interfacing in the actual physical model (the gas inlet is what goes to the natural gas pipeline.) Is that correct? I could also leave it enabled with a baffle type interface which I assume would provide a similar result.

I set up the simulation by setting up 3 parts (pipe, gas, and air) and assigned each part to its own region. Then I did a single mesh for all 3 regions. And made 3 separate physics continua, one for each region. My end goal is to have a velocity distribution of the exhaust in the surrounding air.

Cheers and Thank You

Using: STAR-CCM+ 8.04.007

[Jayhawk]

Update: I've come across the Multi-Component Gas Model so will give that a try setting the "gas" region as 100% mass fraction natural gas and the "air" region as 100% mass fraction air to start with.