If the gas flows out of the inlet boundary,...
 

I'm doing some transient analysis of pipes. If the gas escape from the inlet boundary,what will happen? Can Star-CD deal with this kind problem?

Re: If the gas flows out of the inlet boundary,...
 

If you have outflow you can use inlet or pressure boundary conditions.

Re: If the gas flows out of the inlet boundary,...
 

I've used inlet boundary conditions.It seems that Star-cd hasn't processed the problem.

Re: If the gas flows out of the inlet boundary,...
 

Hi Miles, since upwind scheme has been used, inlet boundary as i see could not handle reverse flow. why not extrude the inlet for a distance.

Re: If the gas flows out of the inlet boundary,...
 

If you mean that you INTEND to use a velocity inlet as outlet boundary (i.e. apply a negative inlet flow - like a suction point) it should be alright. That is if you put a pressure boundary where the flow should enter, to be able to specify turbulent quantities.

Re: If the gas flows out of the inlet boundary,...
 

It seems that Star-CD cannot deal with this problem.

Re: If the gas flows out of the inlet boundary,...
 

It seems to me that you are not able to describe your problem in a way that we know what you are doing and what you intend to do.

Re: If the gas flows out of the inlet boundary,...
 

I'm sorry. I'm trying to simulate the gas flow through pipes. And the boundary conditions is that the flow of the inlet boundary can be positive and negative.

Re: If the gas flows out of the inlet boundary,...
 

You have about 3 possibilities to do this.

1.) use a user defined subroutine and describe the velocity as a function of time

2) use a table with the values of the velocity

3) use the transient calculation with different load steps. For each load step you can select you boundary values and ramp between them.

If you have an analytical function for the vel vs. time the subroutine should be the most straightforward way to go. Otherwise use the second or third way.

Re: If the gas flows out of the inlet boundary,...
 

I'll use the first method. Thank you very much.