Flow not difusing into domain

negarnaghash · February 11, 2019, 16:35

Hi everyone,

I am trying to model a jet flow and I have tried 3D and now I am trying 2D simulation. The problem with the results I get from simulation is the flow does not spread into domain at all like there i a physical wall separating the jet flow from the rest of the domain. The case is turbulent and I am using kOmega model for it (although the laminar setting has the same problem) Also I am running the simulation using rhoCentralFoam solver.

velocity BCs:
inletOutlet for outlet
outletInlet for domain inlet
outletInlet for nozzle inlet
noSlip for nozzleWalls
outletInlet for farfield;

pressure BCs:
zeroGradient for outlet
fixedValue for domain inlet
totalPressure for nozzle inlet
zeroGradient for nozzleWalls
zeroGradient for farfield;

temperature BCs:
inletOutlet for outlet
fixedValue for domain inlet
totalTemperature for nozzle inlet
zeroGradient for nozzleWalls
zeroGradient for farfield;

Does anyone have any idea what can cause this?
I attached a screenshot of the flow here.

sufjanst · February 15, 2019, 06:09

I guess your velocity 8 (and viscosity) is too high or you use the wrong turbulence model. What is your velocity? The flow in your pipe looks like you try to simulate a supersonic flow.

Your flowfield is exactly what I expect from k-omega with high velocities.

negarnaghash · February 15, 2019, 16:50

The velocity is 170 but flow is subsonic with M=0.5 . The flow has a high Re roughly 6 e5. And honestly my understanding is the flow is behaving less viscous than what is supposed to.

How can I have any control on viscosity setups?

And what else may cause this problem I have here?

schuyler · February 15, 2019, 17:55

I would make sure your viscosity is correctly set in your thermoPhysicalProperties file.

Also, for lower speed flows you should have very small residuals if you are using rhoCentralFoam. This is because it is density based. Try reducing them in your fvSolution file. For this flow speed, you could also try sonicFoam which is pressure based.

Are you providing any turbulence coming into the inlet? You could use turbulentIntensityKineticEnergyInlet for k, and turbulentMixingLengthFrequencyInlet for omega.

Finally, if none of those give you the results you expect, try to recreate an experiment or existing simulation from the literature. If it matches, then you know there is nothing wrong with your setup.

mfrl · February 16, 2019, 22:02

Please check the pressure field you computed.

My guess is that the static pressure in your external flow is getting lower and lower while the total conditions of the nozzle inlet are constant.

Mrfl

huangfei · June 3, 2019, 22:36

Hi, have you solved this problem? I face the same thing as you. It looks like existing unphysical pressure wave in the nozzle.

February 15, 2019, 17:55		#4
schuyler Member W. Schuyler Hinman Join Date: Apr 2013 Location: Calgary, Alberta, Canada Posts: 38 Rep Power: 13	I would make sure your viscosity is correctly set in your thermoPhysicalProperties file. Also, for lower speed flows you should have very small residuals if you are using rhoCentralFoam. This is because it is density based. Try reducing them in your fvSolution file. For this flow speed, you could also try sonicFoam which is pressure based. Are you providing any turbulence coming into the inlet? You could use turbulentIntensityKineticEnergyInlet for k, and turbulentMixingLengthFrequencyInlet for omega. Finally, if none of those give you the results you expect, try to recreate an experiment or existing simulation from the literature. If it matches, then you know there is nothing wrong with your setup. __________________ Schuyler

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February 15, 2019, 06:09		#2
sufjanst Member Join Date: Mar 2016 Posts: 73 Rep Power: 10	I guess your velocity 8 (and viscosity) is too high or you use the wrong turbulence model. What is your velocity? The flow in your pipe looks like you try to simulate a supersonic flow. Your flowfield is exactly what I expect from k-omega with high velocities.

February 15, 2019, 16:50		#3
negarnaghash New Member Negar Naghash Join Date: Mar 2017 Posts: 5 Rep Power: 9	The velocity is 170 but flow is subsonic with M=0.5 . The flow has a high Re roughly 6 e5. And honestly my understanding is the flow is behaving less viscous than what is supposed to. How can I have any control on viscosity setups? And what else may cause this problem I have here?

February 16, 2019, 22:02		#5
mfrl New Member MF Join Date: Jan 2019 Posts: 6 Rep Power: 7	Please check the pressure field you computed. My guess is that the static pressure in your external flow is getting lower and lower while the total conditions of the nozzle inlet are constant. Mrfl

June 3, 2019, 22:36		#6
huangfei New Member Bo Kong Join Date: Oct 2016 Location: China Posts: 22 Rep Power: 10	Hi, have you solved this problem? I face the same thing as you. It looks like existing unphysical pressure wave in the nozzle.