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Harry Qiu June 29, 2001 04:56

??????????????
 
Dear Mr. or Ms.:

I am simulating a turbulent flow problem with Standard k-epslon model.My problem setup are as follows: 1. velocity inlet 2. pressure outlet 3. K-Epslon turbulent model

After iteration, I find that the velocity distribution seems right. But the pressure distribution seems wrong, because where the static pressure is large, the velocity pressure is large too. So this results in the total pressure difference between different points is much bigger than I expected.

For example: the fluid flow through a sharp-expansion duct, before the sharp-expansion the total pressure is 20000 Pa, but after the expansion the total pressure is 0 Pa. I think it's a wrong iteration resolution.

But can you tell me why I get this wrong sovlement?

Thank you very much. Any points are welcomed.

Sincerely yours, Harry.


zhou_eric June 29, 2001 05:38

Re: ??????????????
 
Hi Harry, It is seemed that you are interested in the pressure distribution in your problems.The abnormality is due to your boundary conditions. Now that the pressure_outlet is specified, the boundary condition for the inlet should be pressure_inlet instead.

Good luck,

Eric

Scott Whitney June 29, 2001 15:06

Re: ??????????????
 
The standard setup recommended by Fluent is a velocity_inlet and a pressure_outlet. So I do not understand your comments, zhou_eric. Please elaborate.

zhou_eric June 29, 2001 22:31

Re: ??????????????
 
You might just try it firstly, and then get the core of it.

eric

Chetan Kadakia July 1, 2001 01:41

Re: ??????????????
 
I agree, try the pressure inlet b.c. Sometimes this b.c is preferred over the velocity inlet condition due to the problem at hand. One example is when you have considerable compressiblity.

The pressure inlet includes both total and static pressure. But the velocity inlet only takes in the velocity. i don't remember all the equations, but in the case of a pressure inlet, you are giving values to two unknowns versus the velocity inlet where you are giving a value to one unknown.

The more obviuos as previously stated is that where pressure data is concerned, use pressure inlet and pressure outlet conditions.


max July 26, 2001 23:45

Re: ??????????????
 
The total pressure and supersonic/initial gauge pressure are defined at the PRESSURE INLET B.C.However,the supersonic/initial gauge pressure works only when you plan to initial the solution or the flow is supersonic.That is,if M<1,the value you enter as supersonic gauge pressure is ignored! My question is how to set the pressure inlet and pressure outlet B.C if you don't know the pressue drop?Thanks in advance.


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