Nozzle for discharge modeling

prij · February 23, 2016, 20:12

Hi,

I have been using this nozzle whose inlet contains supercritical CO2 and the divergent part of the nozzle is ambient air. So basically, CO2 is passing through a small hole into the atmosphere. I am using Multiphase VOF model (Phase-1 is air and Phase-2 is CO2) with pressure inlet and pressure outlet as BC's. I have set the volume fraction of CO2 as 1 in the inlet and backflow volume fraction in the outlet for CO2 as 0. When I run the simulation and generate results for volume fraction for phase-1(air) and phase-2(CO2), I still observe that the volume fraction is 1 throughout for CO2 case and 0 for air throughout with only changes at the nozzle throat. Even the reference values populated when I give inlet and outlet are not changing. I am confused whether I am using the right method and way. I would appreciate if somebody could guide me with this.

Thanks.

harry123 · May 4, 2016, 04:28

I use VOF method for simulating water jet into air. The problems I encountered for wrong volume fractions along axis for water were:

1. Using small time step when mesh was coarse.
2. Changing inlet velocity profile affected the results.
3. Changing inlet turbulence intensity affected the results.

I'm still working on it, but so far these are the issue I came across.

prij · May 4, 2016, 04:36

Hi,

Thanks for your reply.

Did you get the required momentum for your water jet when it was let out in air? Because in my case it is a gas and the dispersion of CO2 in air was not giving me sufficient momentum to disperse up to great distances. What was the turbulence intensity in your case?

Thanks.

harry123 · May 4, 2016, 05:33

The plot for variation of velocity along axis was matching (though not exactly) with benchmarks, so I guess there is no problem there.

I had used turbulent intensity of 0.01 for my simulations. Using 0.1 gave me results not matching benchmark.

February 23, 2016, 20:12	Nozzle for discharge modeling	#1
prij New Member Join Date: Feb 2016 Posts: 7 Rep Power: 10	Hi, I have been using this nozzle whose inlet contains supercritical CO2 and the divergent part of the nozzle is ambient air. So basically, CO2 is passing through a small hole into the atmosphere. I am using Multiphase VOF model (Phase-1 is air and Phase-2 is CO2) with pressure inlet and pressure outlet as BC's. I have set the volume fraction of CO2 as 1 in the inlet and backflow volume fraction in the outlet for CO2 as 0. When I run the simulation and generate results for volume fraction for phase-1(air) and phase-2(CO2), I still observe that the volume fraction is 1 throughout for CO2 case and 0 for air throughout with only changes at the nozzle throat. Even the reference values populated when I give inlet and outlet are not changing. I am confused whether I am using the right method and way. I would appreciate if somebody could guide me with this. Thanks.

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May 4, 2016, 04:28		#2
harry123 Member Join Date: Aug 2014 Location: Germany Posts: 80 Rep Power: 12	I use VOF method for simulating water jet into air. The problems I encountered for wrong volume fractions along axis for water were: 1. Using small time step when mesh was coarse. 2. Changing inlet velocity profile affected the results. 3. Changing inlet turbulence intensity affected the results. I'm still working on it, but so far these are the issue I came across.

May 4, 2016, 04:36		#3
prij New Member Join Date: Feb 2016 Posts: 7 Rep Power: 10	Hi, Thanks for your reply. Did you get the required momentum for your water jet when it was let out in air? Because in my case it is a gas and the dispersion of CO2 in air was not giving me sufficient momentum to disperse up to great distances. What was the turbulence intensity in your case? Thanks.

May 4, 2016, 05:33		#4
harry123 Member Join Date: Aug 2014 Location: Germany Posts: 80 Rep Power: 12	The plot for variation of velocity along axis was matching (though not exactly) with benchmarks, so I guess there is no problem there. I had used turbulent intensity of 0.01 for my simulations. Using 0.1 gave me results not matching benchmark.