VOF SLOSHING SIMULATION ISSUE with inviscid

navi · February 27, 2017, 00:45

hello, can anyone help me,
how to simulate by assuming liquid is inviscid in some tank oscillation. if I give dynamic viscosity in materials as zero, it is right i am doing to make inviscid simulation,
how to neglect Hydrostatic pressure in liquid tank oscillation

ghorrocks · February 27, 2017, 01:46

You cannot put viscosity =0 in CFX. You need to give it some value. Use a very small number instead, and then check it is effectively inviscid by changing it by a factor of 10 and checking it makes no difference.

Note that an inviscid free surface simulation will have lots of ripples in the surface which will dissipate very slowly. This is never going to converge as a steady state simulation., but you should be OK with a transient simulation.

You cannot "neglect" hydrostatic pressure. When you activate buoyancy mode in CFX it uses a modified pressure value which already has the hydrostatic pressure component removed. Is this what you mean? If so it is activated automatically when you select a buoyant simulation.

navi · February 27, 2017, 02:01

i have done analytical study for pressure distribution in tank (only dynamic pressure). neglecting Static pressure inside tank for liquid height (ro*g*h). same this i need to simulate neglecting static pressure,
how can i do

and also i neglect surface tension, and liquid is inviscid ,
with this assumption , can i simulate .

ghorrocks · February 27, 2017, 02:11

Surface tension is a separate model. You can turn the surface tension model on and off as you like.

As I said before, when you activate the buoyancy model the pressure variable already has the hydrostatic component removed. So what you are asking for is already there.

navi · February 27, 2017, 02:19

which turbulence model can select for inviscid, low viscosity of fluid,
in post processing can i measure pressure for different liquid height (means i have 0.25 m liquid height i need pressure in every position of in this height like pressure at 0.2 m, 0.1m etc.

ghorrocks · February 27, 2017, 05:59

Turbulence models are meaningless in inviscid flows. If you are inviscid you should be using a laminar flow model.

Your second question is just basic post processing. This is easily done in CFD-Post.

navi · February 27, 2017, 06:10

Quote:

Originally Posted by ghorrocks

Your second question is just basic post processing. This is easily done in CFD-Post.

i tried i didn't get at particular point, il get pressure at wall full surface. and also i tried by making points at particular height and checked pressure, but point i can not select.

any link in CfD form for post processing the pressure distribution

ghorrocks · February 27, 2017, 06:52

Have you done the CFX tutorial examples? It shows you how to do basic post processing. You can download them on the ANSYS Customer page.

February 27, 2017, 00:45	VOF SLOSHING SIMULATION ISSUE with inviscid	#1
navi Member naveen kumar s Join Date: Aug 2016 Location: india, bengalore Posts: 51 Rep Power: 10	hello, can anyone help me, how to simulate by assuming liquid is inviscid in some tank oscillation. if I give dynamic viscosity in materials as zero, it is right i am doing to make inviscid simulation, how to neglect Hydrostatic pressure in liquid tank oscillation

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February 27, 2017, 01:46		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	You cannot put viscosity =0 in CFX. You need to give it some value. Use a very small number instead, and then check it is effectively inviscid by changing it by a factor of 10 and checking it makes no difference. Note that an inviscid free surface simulation will have lots of ripples in the surface which will dissipate very slowly. This is never going to converge as a steady state simulation., but you should be OK with a transient simulation. You cannot "neglect" hydrostatic pressure. When you activate buoyancy mode in CFX it uses a modified pressure value which already has the hydrostatic pressure component removed. Is this what you mean? If so it is activated automatically when you select a buoyant simulation.

February 27, 2017, 02:01		#3
navi Member naveen kumar s Join Date: Aug 2016 Location: india, bengalore Posts: 51 Rep Power: 10	i have done analytical study for pressure distribution in tank (only dynamic pressure). neglecting Static pressure inside tank for liquid height (rogh). same this i need to simulate neglecting static pressure, how can i do and also i neglect surface tension, and liquid is inviscid , with this assumption , can i simulate .

February 27, 2017, 02:11		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	Surface tension is a separate model. You can turn the surface tension model on and off as you like. As I said before, when you activate the buoyancy model the pressure variable already has the hydrostatic component removed. So what you are asking for is already there.

February 27, 2017, 02:19		#5
navi Member naveen kumar s Join Date: Aug 2016 Location: india, bengalore Posts: 51 Rep Power: 10	which turbulence model can select for inviscid, low viscosity of fluid, in post processing can i measure pressure for different liquid height (means i have 0.25 m liquid height i need pressure in every position of in this height like pressure at 0.2 m, 0.1m etc.

February 27, 2017, 05:59		#6
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	Turbulence models are meaningless in inviscid flows. If you are inviscid you should be using a laminar flow model. Your second question is just basic post processing. This is easily done in CFD-Post.

February 27, 2017, 06:52		#8
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	Have you done the CFX tutorial examples? It shows you how to do basic post processing. You can download them on the ANSYS Customer page.