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Note: This discussion is about an older version of the COMSOL Multiphysics® software. The information provided may be out of date.

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Dimensionless in comsol

Posted 2015年7月9日 GMT-4 00:01 Computational Fluid Dynamics (CFD) Version 4.4 3 Replies

Leo Mechelle
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Hi Everyone,

I have a question about the dimensionless in comsol. If we choose none in unit system and then add module like laminar flow, we need to fill in the density and viscosity in fluid properties. However, the density and viscosity are all in SI unit (default setting). I wonder how to set these two with dimensionless unit instead of the SI unit?
Many THanks!

Best,
Leo
3 Replies Last Post 2015年7月9日 GMT-4 06:14
Lasse Murtomäki
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Posted: 9 years ago 2015年7月9日 GMT-4 05:01
When you chooce dimensionless form, also units should appear dimensionless, at least with me that happens. But the equation has to be converted dimensionless that you know what you are actually simulating.

Attached one way of doing it; the boundary conditions must then be converted accordingly.

br
Lasse
When you chooce dimensionless form, also units should appear dimensionless, at least with me that happens. But the equation has to be converted dimensionless that you know what you are actually simulating. Attached one way of doing it; the boundary conditions must then be converted accordingly. br Lasse
Lasse Murtomäki
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Posted: 9 years ago 2015年7月9日 GMT-4 05:08
Typo: Also pressure nabla should be nabla prime.

With these definitions the coefficients take the value 1.
Typo: Also pressure nabla should be nabla prime. With these definitions the coefficients take the value 1.
Leo Mechelle
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Posted: 9 years ago 2015年7月9日 GMT-4 06:14
Dear Lasse,

Thank you so much for your reply. My understanding from your advices is that when Comsol solve N-S equations, the quantities should be dimentionless with the use of density and viscosity instead of other values.
Thank you so much!

Best,
Leo
Dear Lasse, Thank you so much for your reply. My understanding from your advices is that when Comsol solve N-S equations, the quantities should be dimentionless with the use of density and viscosity instead of other values. Thank you so much! Best, Leo

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