Pressure_Inlet with constant inlet velocity?

Sandra_ · February 6, 2014, 09:55

Hello,

I am running many simulations, using different values for the boundary 'pressure_inlet' . I want the inlet axial velocity to have the same value for all simulations. How can I realize this?

pleeeeaaase help me!

regards
Sandra

gfoam · February 6, 2014, 13:04

Can you specify what kind of simulation are you trying to do? Compressible or incompressible? What geometry? But in the case of pressure inlet you specify a stagnation or total pressure an a static pressure (and if your problem is compressible then you must set the total pressure), the the flow conditions at inlet are computed with the isentropic formulations. But if you want more detail, please read the chapter 6 of FLUENT's User Guide

Sandra_ · February 7, 2014, 09:40

Hello gfoam,

thank you for your answer!
A pressure-based flow is running through a simple sharp edged orifice. I am using a multiphase and a cavitation model. Standard k-epsilon turbulence model and wall function.
I specify a gauge total pressure and the supersonic/initial gauge pressure, normal to boundary . (actually I copied all settings from the tutorial: modeling cavitation).

When I check on my results the gauge total pressure I entered is the static pressure at the inlet. The supersonic/initial gauge pressure I set to zero because it has no influence on the intial velocity. I tried different values and always got the same values for the velocity.

I don't know how I can specify a constant inlet velocity (without using a velocity inlet boundary) for all my simulations.

Sandra_ · February 8, 2014, 14:26

Is it even possible to specify a value for the inlet velocity, using a pressure_inlet and pressure_outlet boundary condition?

If I write a UDF or a Profile it's only possible to use then when I have a velocity_inlet boundary condition.

Any help? Pleaase

Sandra_ · February 8, 2014, 14:29

I also tried to patch it during the initialization but it didn't work either..

gfoam · February 10, 2014, 05:56

OK, acording to th User's Guide when you specify a Pressure Inlet BC, in subsonic flow you have to set the total perssure and a initial gauge pressure, so as you can see the initial condition is only used to initialize the flow (§6.3.3.1.1.4. Defining Static Pressure of User's Guide). So if you can change the velocity of your simulation, you must change tho outlet pressure, but you can't calculate in advance what velocity you get at the inlet, that's why if you want to specify the velocity at the inlet you must use Velocity Inlet BC's. I hope this helps you. Regards.
Gonzalo

February 6, 2014, 09:55	Pressure_Inlet with constant inlet velocity?	#1
Sandra_ New Member Join Date: Dec 2013 Posts: 4 Rep Power: 12	Hello, I am running many simulations, using different values for the boundary 'pressure_inlet' . I want the inlet axial velocity to have the same value for all simulations. How can I realize this? pleeeeaaase help me! regards Sandra

February 7, 2014, 09:40	Thanks	#3
Sandra_ New Member Join Date: Dec 2013 Posts: 4 Rep Power: 12	Hello gfoam, thank you for your answer! A pressure-based flow is running through a simple sharp edged orifice. I am using a multiphase and a cavitation model. Standard k-epsilon turbulence model and wall function. I specify a gauge total pressure and the supersonic/initial gauge pressure, normal to boundary . (actually I copied all settings from the tutorial: modeling cavitation). When I check on my results the gauge total pressure I entered is the static pressure at the inlet. The supersonic/initial gauge pressure I set to zero because it has no influence on the intial velocity. I tried different values and always got the same values for the velocity. I don't know how I can specify a constant inlet velocity (without using a velocity inlet boundary) for all my simulations.

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February 6, 2014, 13:04		#2
gfoam Senior Member Gonzalo Join Date: Mar 2011 Location: Argentina Posts: 122 Rep Power: 16	Can you specify what kind of simulation are you trying to do? Compressible or incompressible? What geometry? But in the case of pressure inlet you specify a stagnation or total pressure an a static pressure (and if your problem is compressible then you must set the total pressure), the the flow conditions at inlet are computed with the isentropic formulations. But if you want more detail, please read the chapter 6 of FLUENT's User Guide

February 8, 2014, 14:26		#4
Sandra_ New Member Join Date: Dec 2013 Posts: 4 Rep Power: 12	Is it even possible to specify a value for the inlet velocity, using a pressure_inlet and pressure_outlet boundary condition? If I write a UDF or a Profile it's only possible to use then when I have a velocity_inlet boundary condition. Any help? Pleaase

February 8, 2014, 14:29		#5
Sandra_ New Member Join Date: Dec 2013 Posts: 4 Rep Power: 12	I also tried to patch it during the initialization but it didn't work either..

February 10, 2014, 05:56		#6
gfoam Senior Member Gonzalo Join Date: Mar 2011 Location: Argentina Posts: 122 Rep Power: 16	OK, acording to th User's Guide when you specify a Pressure Inlet BC, in subsonic flow you have to set the total perssure and a initial gauge pressure, so as you can see the initial condition is only used to initialize the flow (§6.3.3.1.1.4. Defining Static Pressure of User's Guide). So if you can change the velocity of your simulation, you must change tho outlet pressure, but you can't calculate in advance what velocity you get at the inlet, that's why if you want to specify the velocity at the inlet you must use Velocity Inlet BC's. I hope this helps you. Regards. Gonzalo