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-   -   Gravity in vertical pipe (http://www.cfd-online.com/Forums/fluent/96331-gravity-vertical-pipe.html)

jpo January 19, 2012 15:08

Gravity in vertical pipe
 
Hello,

does someone know how to run Fluent simulation of a vertical pipe with gravity on?

I don't see any difference in the flow when gravity is enabled...


Many thanks

delaneyluke January 20, 2012 01:57

Could you provide more details, like your BC's and fluid used, single or multi phase.

Amir January 20, 2012 04:07

Quote:

Originally Posted by jpo (Post 340172)
Hello,

does someone know how to run Fluent simulation of a vertical pipe with gravity on?

I don't see any difference in the flow when gravity is enabled...


Many thanks

Dear friend,

If you don't have pressure BC in incompressible flow fields, including gravity doesn't change the flow field; because you can introduce new pressure variable numerically which includes the gravity term. Obviously, you can find the original pressure field by excluding the added field.

Bests,

Sixkillers January 20, 2012 04:45

If you want to see effect of hydrostatic pressure, which depends on gravity, in a pressure field try set the operating density to zero (Cell zone conditions -> Operating conditions -> Specified operating density).

jpo January 20, 2012 14:42

Thank you for the suggestion to set the operating density to zero; it seems to work well now

Thank you for your replies

ComputerGuy January 20, 2012 15:01

(Please delete my message -- wrong post)

Quote:

Originally Posted by jpo (Post 340172)
Hello,

does someone know how to run Fluent simulation of a vertical pipe with gravity on?

I don't see any difference in the flow when gravity is enabled...


Many thanks


jpo January 20, 2012 15:04

It is single phase; just trying to see if the "gravity" option makes a difference in the pressures in a pipe

As a next step I am contemplating to write a UDF to try and modify the gravity vector. Would someone know how to to this?

ComputerGuy January 20, 2012 15:15

Are you talking about modifying the gravity vector as the simulation proceeds, or modification to be something other than -9.81 m/s^2 in the "down" direction? If you're looking at simply modifying it from -9.81, this is what you're specifying in the X, Y, and Z components of gravity when you turn it "on." Instead of -9.81 in the Z direction, if you make it -9.81 in the Y direction, gravity will now be "sideways" instead of "down" as in your previous case.

ComputerGuy

Quote:

Originally Posted by jpo (Post 340360)
It is air only; just trying to see if the "gravity" option makes a difference in the pressures in a pipe

As a next step I am contemplating to write a UDF to try and modify the gravity vector. Would someone know how to to this?


jpo January 20, 2012 15:19

Gravity will be rigidly defined for the entire simulation, but want to make it vary with altitude


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