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Ng T. H. Bernard December 15, 1998 09:13

hi..... i am a FLUENT v4.3 software user i want to model a unsteady flow in a uniform pipe. An 2D axissymetrical model was used

At the inlet of the pipe , i specify INLET and assuming a developed flow at inlet, i want to vary the velocity of flow wrt time and dist from the pipe center. However, i can only vary the velocity wrt dist and not time..... Is this the limitation of the software or is there other ways to model the varying velocity profiles?? at the outlet of pipe, i specify OUTLET and at the pipe center as SYMMETRY.

Thanks you bernard

Essemiani December 16, 1998 06:04

I think that you can use varying boundary conditions ( time or geometrical position) ,have a look in:

Expert/modeling-options/ allow profile setting ---YES

Your boudaries are well defined ( Inlet, outlet, symmetry ).

Good luck


bernard December 17, 1998 02:08

hi Essemian... thanks for replying.....really appreciate it.... however....i think i can't get it.... to better understand my problem......will elaborate more I want to input sine wave velocity with a developed velocity profile at the inlet......and since this is a time -dependent problem .....i need to enable the time dependent model right????

assuming i have done with the material properties, next will be the INLET conditions.....which i will go to the inlet and specify harmonic velocity......and select velocity in terms of either y or u(y) or u(t) with the necessary coefficent. if i select u(t) , then the velocity is of same magnitude at the inlet but vary with time but does not vary with y.....hence not able to get a developed velocity profile at the inlet.... please advice.... yorus sincerely bernard

Essemiani December 18, 1998 09:22

Hi ,

Please correct me if i make a mistake , i think that you need to have U= function (y,t)at the inlet .

The solution is to use multiple inlets i mean if you have an inlet with 4 cells trasform it in 4 different inlets ( i1,1i2,i3,i4) and in every inlet you will just take U)function( Constant, t) , where constant is related to y position

Good luck


Md. Shahiduzzaman Khan February 14, 1999 11:37

Hi! I am using Fluent Uns/Rampant. It's possible to write a user define function for the inlet velocity which will vary with time. So I think it's also possible in Fluent v4.3. Khan

Ali Oge February 16, 1999 07:50


Yes, you can define time dependent inlet boundary conditions, for example sinusoidal inlet velocity, by using User-Defined Functions. It is easy and flexible. If you have FLUENT/UNS User's guides, there are examples. If you don't have I can send some examples.


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