How to suppress convection & viscous effects using CFX

Haga · January 17, 2011, 21:40

In a free surface transient flow problem of a fluid in a partially filled container, how can one reduce or suppress the effect of convection & viscosity theoretically & using CFX?? Is it possible to achieve this simultaneously or would there be a need of compromising anything to achieve this condition?

ghorrocks · January 18, 2011, 19:18

You cannot model inviscid flows in CFX, but you can specify a viscosity so low that it is effectively zero. This is easy, but may cause convergence problems especially for free surface problems.

CFX is a Navier Stokes solver so solution of convection is inherent. I cannot see how a free surface simulation could be driven by diffusion only. Can you explain why you want to stop convection?

Haga · January 31, 2011, 21:09

1st of all...Thanks for replying...

Viscous effects as u said can be controlled so. But what is the use of convective term in a free surface problem of a liquid inside a container? If it was flowing, then convective effects can be considered. Since there's no liquid motion other than oscillation why it is that the convective effect be kept considered while doing the model?

ghorrocks · February 1, 2011, 18:31

If the fluid is moving then convective effects are contributing. If the fluid is not moving then forget CFD and it work out by far simpler methods.

So what are you trying to do?

January 17, 2011, 21:40	How to suppress convection & viscous effects using CFX	#1
Haga New Member Hareesh R Iyer Join Date: Dec 2010 Location: Thiruvananthapuram Posts: 21 Rep Power: 15	In a free surface transient flow problem of a fluid in a partially filled container, how can one reduce or suppress the effect of convection & viscosity theoretically & using CFX?? Is it possible to achieve this simultaneously or would there be a need of compromising anything to achieve this condition?

January 31, 2011, 21:09	@ Glenn	#3
Haga New Member Hareesh R Iyer Join Date: Dec 2010 Location: Thiruvananthapuram Posts: 21 Rep Power: 15	1st of all...Thanks for replying... Viscous effects as u said can be controlled so. But what is the use of convective term in a free surface problem of a liquid inside a container? If it was flowing, then convective effects can be considered. Since there's no liquid motion other than oscillation why it is that the convective effect be kept considered while doing the model?

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January 18, 2011, 19:18		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	You cannot model inviscid flows in CFX, but you can specify a viscosity so low that it is effectively zero. This is easy, but may cause convergence problems especially for free surface problems. CFX is a Navier Stokes solver so solution of convection is inherent. I cannot see how a free surface simulation could be driven by diffusion only. Can you explain why you want to stop convection?

February 1, 2011, 18:31		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	If the fluid is moving then convective effects are contributing. If the fluid is not moving then forget CFD and it work out by far simpler methods. So what are you trying to do?