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-   -   Back Flow problem (http://www.cfd-online.com/Forums/openfoam-solving/84475-back-flow-problem.html)

siddharameshwara January 31, 2011 08:29

Back Flow problem
 
Hello to all,

I am trying to simulate diesel flow in the nozzle of injector. I used inletOutlet boundary condition at the outlet for the velocity and fixedMeanValue at the outlet for pressure. I am using icoFoam solver , pisoFoam solver and cavitatingFoam solver. For the first two i have no problem but for the cavitatingFoam solver at the outlet of the nozzle :(reverse flow:( of the Diesel is taking place. Could any one help me is the boundary condition that i have used is right one?? and how can i avoid the reverse flow??? even i tried with extruding the outlet but it dosent work

Thanks in advance.

Zowie February 9, 2011 06:32

If you have back flow and you are using inletOutlet, then you need to define the inletValue as (0,0,0). With this, you will avoid the back flow at the outlet.
Have a look at the code of the BC to see how it works.:o

siddharameshwara February 16, 2011 12:07

Hi,

Yes i have set the inletValue as said by you. Even though problem is not solved. Could you please tell me the reason why backflow is occuring ??? is it physical one or boundary condition code mistake????

Zowie February 16, 2011 14:57

Well, I can't tell you the reason because I don't know exactly the problem you are dealing with...:o but from what I can infer from your post the flow is probably cavitating and vapour reaches the outlet... if you have back flow it might be because the pressure inside the domain is lower than the pressure at the outlet patch.

If you use inletOutlet with inlet value (0 0 0) you shouldn't have backflow. Try to post a picture of the velocity vectors perpendicular to the outlet patch so that we can see the back flow.

siddharameshwara February 17, 2011 03:34

2 Attachment(s)
Hi,

My case is to simulate the diesel flow in the nozzle of the injector. You are right it is cavitating. It is cavitating in the extended pipe like structure. My model is in the attachment.

My boundary consitions are as follows

0/p file:

INLET3
{
type totalPressure;
U U;
phi phi;
rho none;
psi none;
gamma 1;
p0 uniform 1100000;
value uniform 1100000;
}
OUTLET4
{

type fixedMeanValue;
meanValue 100000;

}


and 0/U file:

INLET3
{
type zeroGradient;
}
OUTLET4
{


type inletOutlet;
inletValue uniform (0 0 0);
value uniform (0 0 0);

}

second image is velocity vectors at the outlet

Zowie February 21, 2011 14:42

I see the backflow... that is very strange... I also use this boundary condition quite often and I never had this problem.

Have you already checked the source code of the boundary condition? It is useful for ensuring that the boundary does what you expect.

I'll have a look into it when I find time (not in the next days, probably...:()

siddharameshwara February 22, 2011 06:22

Hi,

Not yet. I will go through it. May be in few days!!! I am not good at these stuffs please let me know if you find something strange!!!!


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