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What is the difference between freestream BC and inletoutlet BC |
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September 10, 2018, 02:12 |
What is the difference between freestream BC and inletoutlet BC
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#1 |
Member
ijaz fazil
Join Date: Apr 2013
Location: Singapore
Posts: 73
Rep Power: 13 |
Dear all
I'm confused how freestream bc differs from normal inletoulet BC Based on my readings Freestream BC freestream BC has the type inlet/outlet meaning that it looks locally (forevery face of the patch) at the mass flow rate. If the flow is going outside the boundary will be locally zero gradient, if it is going inside the boundary will be locally fixedValue. This boundary condition provides a free-stream condition. It is a ’mixed’ condition derived from the inletOutlet condition, whereby the mode of operation switches between fixed (free stream) value and zero gradient based on the sign of the flux inletoutlet The inletOutlet boundary condition is normally the same as zeroGradient, but it switches to fixedValue if the velocity vector next to the boundary aims inside the domain (backward flow). The value of that fixedValue is inletValue. See figure (). (source: https://www.cfdsupport.com/OpenFOAM-...t/node114.html) Then how Freestream BC differs or modified from conventional inletoutlet BC? |
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June 14, 2019, 07:06 |
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#2 |
New Member
Arslan Adeel Ur Rehmann
Join Date: Jun 2018
Posts: 9
Rep Power: 8 |
Hi.
I am also wandering the same. Did you get any clear reason for the fundamental difference between these two BC's. Thanks |
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June 14, 2019, 07:28 |
not sure
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#3 |
Member
ijaz fazil
Join Date: Apr 2013
Location: Singapore
Posts: 73
Rep Power: 13 |
In general if I post about this question in other forum also
Researchers try to differentiate between general freestream and inlet outlet Not specific to openfoam. What I noticed is, depending on the pressure difference inside the domain either the flow enters or leaves the domain "freestream boundary condition works). For example in a openchannel water flow modelling, I know only the inlet velocity for water and for air I use freestream InletOutlet mostly at outlet condition This was the reply I got it from cfdsupport Dear Dr. Ijaz Fazil, the answer is very simple: freestream and inletOutlet boundary conditions are very the same. They are switching fixedValue and zeroGradient with respect to the sign of the flux. freestreamVelocity and freestreamPressure differ a little bit = switching (or exactly blending) between fixedValue and zeroGradient is driven by the velocity orientation. Have a nice weekend! Radek Your CFD Support Helpdesk Team, Dear Dr. Fazil, the freestream boundary condition enables you to use field as a freestreamValue, whereas inletOutlet uses inletValues, that is constant for the whole patch. Other than that, they are the same. Best regards, Vojtech Prihoda Your CFD Support Helpdesk Team, |
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May 19, 2020, 11:20 |
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#4 | ||
New Member
Arash
Join Date: May 2017
Posts: 17
Rep Power: 9 |
Quote:
freestream (as well as inletOutlet or outletInlet) They are either a Dirichlet and Neumann BC based on the flux direction. The condition for freestream and inletOutlet are the same (equating the value of the parameter to the given freestreamValue or inletValue in case of an inflow and zero-grad otherwise) because they are usually considered as output BC. On the contrary, since outletInlet is used mostly as input, it becomes zero-grad when the inflow occurs. freestreamVelocity and freestreamPressure They are in fact Robine BC as the openFoam blends the values from one condition to another (again using the same conditions). Quote:
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boundary condition, freestream, inletoutlet, openfoam |
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