Negative pressure value

sar_mech · November 19, 2010, 09:12

Dear All,

I am working on a transient state type problem,when i printed the summary of volume averaged static pressure, total pressure, of the fluid flowing into the system, i was surprised to see a negative value.

I could not understand, what does it trying to say,does it mean there is no pressure developed or does it mean there is negative pressure developed, vaccum is created.

I kindly request someone to give a little bit of help on the above problem.

thx...

otd · November 19, 2010, 10:10

What code are using? Commercial? Your own? Something else?

Are you simulating flow of a compressible fluid or incompressible?

If incompressible, the pressure level doesn't matter, only the pressure difference. Compressible flow of course ties the pressure to the density, etc. through some equation of state.

If your flow is assumed incompressible, check your code's documentation to determine what pressure based is used to set up the initial conditions.

Hope this helps.

sar_mech · November 19, 2010, 10:57

Hi I am using Fluent-CFD solver,
my flow is compressible...
could you please tell me is that ok to get negative pressure in the volume average valus of pressure in the fluid zones.
Also if I check in cotours,the max. pressure value is in positive, which value should i have to consider?

thx..

otd · November 19, 2010, 11:31

Check your Fluent documentation. Do they report absolute pressure or some gauge or scaled pressure? A quick call to their help desk might help you as well.

A negative absolute pressure just won't work (even a vacuum has a positive absolute pressure!)

Hope you can get this resolved.

November 19, 2010, 09:12	Negative pressure value	#1
sar_mech New Member saravanakumar Join Date: Mar 2009 Location: United Kingdom Posts: 17 Rep Power: 17	Dear All, I am working on a transient state type problem,when i printed the summary of volume averaged static pressure, total pressure, of the fluid flowing into the system, i was surprised to see a negative value. I could not understand, what does it trying to say,does it mean there is no pressure developed or does it mean there is negative pressure developed, vaccum is created. I kindly request someone to give a little bit of help on the above problem. thx...

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November 19, 2010, 10:10		#2
otd Member private Join Date: Mar 2009 Posts: 74 Rep Power: 17	What code are using? Commercial? Your own? Something else? Are you simulating flow of a compressible fluid or incompressible? If incompressible, the pressure level doesn't matter, only the pressure difference. Compressible flow of course ties the pressure to the density, etc. through some equation of state. If your flow is assumed incompressible, check your code's documentation to determine what pressure based is used to set up the initial conditions. Hope this helps.

November 19, 2010, 10:57		#3
sar_mech New Member saravanakumar Join Date: Mar 2009 Location: United Kingdom Posts: 17 Rep Power: 17	Hi I am using Fluent-CFD solver, my flow is compressible... could you please tell me is that ok to get negative pressure in the volume average valus of pressure in the fluid zones. Also if I check in cotours,the max. pressure value is in positive, which value should i have to consider? thx..

November 19, 2010, 11:31		#4
otd Member private Join Date: Mar 2009 Posts: 74 Rep Power: 17	Check your Fluent documentation. Do they report absolute pressure or some gauge or scaled pressure? A quick call to their help desk might help you as well. A negative absolute pressure just won't work (even a vacuum has a positive absolute pressure!) Hope you can get this resolved.