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Lucas Souza

Mass flux for outflow BC

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I want to simulate a geometry using Acusolve (AcuConsole) and I have a condition of mass flux for my outflow boundary, how can setup like this? The Acu Console only gives me the option of pressure values. Thank you.

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You can do that using Integrated Boundary Conditions.

In AcuConsole click on BC* in the data tree, to navigate to this option.

 

(AcuConsole gives pressure inlet as simple BC, due to stability reasons. There are lots other options available under advanced).

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If this is a problem with a single inlet and a single outlet, it's much better to use mass flow rate (mass flux) as the inflow type and use the standard outflow for the outlet.  The mass flux boundary condition also imposes a profile, which is adding additional constraints that may not be desired at the outlet.

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hello Users!

I am trying to impose the mass flux to the outflow Boundary as well. I have heard that it might bring stability problem to my solution. Any other alternative?

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On 8/14/2019 at 3:38 PM, MADA said:

hello Users!

I am trying to impose the mass flux to the outflow Boundary as well. I have heard that it might bring stability problem to my solution. Any other alternative?

Could you please describe the exact setup?

What data is available to you? Inlet, Outlet, Mass Flux, Pressure, Velocity?

 

Generally MassFlux at inlet or volume flow rate or velocity at inlet and pressure at outlet is the stable configuration. This is also the default or so called SBD = Simple Boundary Condition  in AcuSolve.

MassFlux at outlet is possible under adavanced boudnary conditions.

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On 8/15/2019 at 10:08 AM, ydigit said:

Could you please describe the exact setup?

What data is available to you? Inlet, Outlet, Mass Flux, Pressure, Velocity?

 

Generally MassFlux at inlet or volume flow rate or velocity at inlet and pressure at outlet is the stable configuration. This is also the default or so called SBD = Simple Boundary Condition  in AcuSolve.

MassFlux at outlet is possible under adavanced boudnary conditions.

Thank you for your reply. 

The only available data for me on outflow is mass flux. It was not really clear for me what are differences between Integrated Boundary condition and element boundary condition under advanced option. Do you have any more information regarding to that?

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Do you have multiple inlets and/or outlets?  Can you give the number of inlets and outlets?

 

I'm trying to get clarification on Element BC with a mass flux (or mass flow rate) value.  I think it was only available with Integrated BC previously...

 

Are you using AcuConsole or HyperMesh?

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14 hours ago, acupro said:

Do you have multiple inlets and/or outlets?  Can you give the number of inlets and outlets?

 

I'm trying to get clarification on Element BC with a mass flux (or mass flow rate) value.  I think it was only available with Integrated BC previously...

 

Are you using AcuConsole or HyperMesh?

Hi, 

I have multiple inlets and outlets and I am using AcuConsole.

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I'm guessing that there's an inconsistency in AcuConsole, where a value can be input for mass flow rate in the EBC.  I would suggest you use the Integrated BC.  For an outflow, the value would be positive, whereas for inflow, the value would be negative.  (The definition includes the surface normal.)  Best practice for such a situation is to use Simple BC with type = outflow, then add the Integrated BC and the mass flux option.

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On 8/22/2019 at 7:02 PM, acupro said:

I'm guessing that there's an inconsistency in AcuConsole, where a value can be input for mass flow rate in the EBC.  I would suggest you use the Integrated BC.  For an outflow, the value would be positive, whereas for inflow, the value would be negative.  (The definition includes the surface normal.)  Best practice for such a situation is to use Simple BC with type = outflow, then add the Integrated BC and the mass flux option.

If i want to use both simple BC and integrated BC to impose the mass flux at outflow , which pressure value should I use under the simple BC as I don t know the pressure distribution in outflow? 

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Assuming you're not running ideal gas, etc, and only interested in relative pressure differences, the default pressure = 0 should be fine.  And you can use that at all the outlets where you have Simple BC outflow and integrated BC mass flux.

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13 minutes ago, acupro said:

Assuming you're not running ideal gas, etc, and only interested in relative pressure differences, the default pressure = 0 should be fine.  And you can use that at all the outlets where you have Simple BC outflow and integrated BC mass flux.

The running fluid is air, what is the difference between the air and air-HM?

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They may have slightly different default density and viscosity values.  You'll need to make sure whichever you choose to use, that the material properties are correct for your operating conditions.

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Hi, 

I am trying to  impose 0 relative pressure to inflow and out flow but acusolve gives the the following pressure: 

acuPrep: Processing SIMPLE_BOUNDARY_CONDITION( "TC-Intake" )
acuPrep: *** ERROR: Kinetic energy must be non-zero at inflow boundaries.
acuPrep: *** ERROR: Dissipation rate must be non-zero at inflow boundaries.

 

does anyone know which kind of pressure Acusolve use for the BC? does the pressure indicate absolute pressure or relative one?How can I impose the 0 relative pressure in both intake and outlet?

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Could you post you .inp file?

If not, try: 

- set Stagnation pressure at inlet. 

- setup Turbulent intensity, velocitcy and length scale, depending upon your geometry.

image.png

 

 

 

image.png

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