meassured inlet velocity differs from initial

Supersale · March 20, 2015, 02:29

Hello everyone
I am sumulating a continuous ink-jet using the interFoam solver in OpenFOAM 2.1.1. The geometry is very simple: a cylinder. The cylinder is filled with air and one base is a wall with a no-slip boundary condition applied and on the same base there is also an orifice with the inlet of the ink. The ink is set to flow into the air region with a harmonically changing velocity which is uniform across the radius.
The problem is when i use the "plot over line" tool on the inlet of the ink (the one with the uniform velocity distribution), the meassured distribution is not completely uniform. For the most part it behaves correct and, when moving from the center to the edge of the orifice, on the last cell the velocity drops for some 20%.
Why might that be so?

I also tried to attach a short nozzle to the model with a slip codition inside it, and i also tried combinations where the outer wall has also a slip condition but the results were alwas the same; the velocity drops close to the edge.
The model is axi-symetric.

Thanks in advance.

Svensen · March 21, 2015, 03:10

Please check that you select a point on the inlet patch. It seams that you select the point in the internal field. You can select patches and hide internalField in the paraview

Supersale · March 22, 2015, 19:32

You are right, chosing the inlet patch gives me the appropriate results. You have any idea why i don' get the same in the case with the nozzle and with a slip conditionon the nozzle walls? I guess it's the effect of the outside air but maybe i'm doing something wrong as well?
Anyway, thanks for the reply!

March 20, 2015, 02:29	meassured inlet velocity differs from initial	#1
Supersale New Member Sasa Goran Join Date: Feb 2015 Location: Japan Posts: 23 Rep Power: 11	Hello everyone I am sumulating a continuous ink-jet using the interFoam solver in OpenFOAM 2.1.1. The geometry is very simple: a cylinder. The cylinder is filled with air and one base is a wall with a no-slip boundary condition applied and on the same base there is also an orifice with the inlet of the ink. The ink is set to flow into the air region with a harmonically changing velocity which is uniform across the radius. The problem is when i use the "plot over line" tool on the inlet of the ink (the one with the uniform velocity distribution), the meassured distribution is not completely uniform. For the most part it behaves correct and, when moving from the center to the edge of the orifice, on the last cell the velocity drops for some 20%. Why might that be so? I also tried to attach a short nozzle to the model with a slip codition inside it, and i also tried combinations where the outer wall has also a slip condition but the results were alwas the same; the velocity drops close to the edge. The model is axi-symetric. Thanks in advance.

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March 21, 2015, 03:10		#2
Svensen Senior Member Join Date: Jan 2015 Posts: 150 Rep Power: 11	Please check that you select a point on the inlet patch. It seams that you select the point in the internal field. You can select patches and hide internalField in the paraview

March 22, 2015, 19:32		#3
Supersale New Member Sasa Goran Join Date: Feb 2015 Location: Japan Posts: 23 Rep Power: 11	You are right, chosing the inlet patch gives me the appropriate results. You have any idea why i don' get the same in the case with the nozzle and with a slip conditionon the nozzle walls? I guess it's the effect of the outside air but maybe i'm doing something wrong as well? Anyway, thanks for the reply!