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acceleration due to gravity Laminar flow

Posted Apr 30, 2013, 11:47 p.m. EDT Version 4.2a 2 Replies

Ali
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I want to give acceleration due to gravity effects to fluid in Laminar pipe flow, any one know how to give,?????

I have tried by applying domain volume force like 9.81*density of fluid but i am not sure it is right ???


any suggestions??
2 Replies Last Post May 1, 2013, 3:29 a.m. EDT
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago May 1, 2013, 2:20 a.m. EDT
Hi

what is wrong by adding a "body force" like that ? use the internal "g_const" for the gravity acceleration see help "physical constants"

but think of your model i.e. in 2D-axi you can only simulate gravity along the vertical +/- Z direction, as otherwise you add a radial force, hence you are in a special rotating tube case

un CFD still you have also the pressure build-up with height (along gravity vector direction as Dp = g_const*rho*(z-z0)

COMSOL acts on the infinitesimal element volume dx*dy*dz so if you multiply

integral_over_domain g_const*rho*dx*dy*dz you get to the force in Newton [N=m/s^2*kg/m^3*m*m*m ]

--
Good luck
Ivar
Hi what is wrong by adding a "body force" like that ? use the internal "g_const" for the gravity acceleration see help "physical constants" but think of your model i.e. in 2D-axi you can only simulate gravity along the vertical +/- Z direction, as otherwise you add a radial force, hence you are in a special rotating tube case un CFD still you have also the pressure build-up with height (along gravity vector direction as Dp = g_const*rho*(z-z0) COMSOL acts on the infinitesimal element volume dx*dy*dz so if you multiply integral_over_domain g_const*rho*dx*dy*dz you get to the force in Newton [N=m/s^2*kg/m^3*m*m*m ] -- Good luck Ivar
Ali
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Posted: 1 decade ago May 1, 2013, 3:29 a.m. EDT
Thanks alot Ivar, my problem is 3D and i think your help worked me
Thanks alot Ivar, my problem is 3D and i think your help worked me

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