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-   -   Pressure waves bouncing around while using coodles (http://www.cfd-online.com/Forums/openfoam-solving/59078-pressure-waves-bouncing-around-while-using-coodles.html)

ankgupta8um February 27, 2008 21:30

Hello, I am using coodles s
 
Hello,

I am using coodles solver to simulate the expansion of annular jet into a cylinder. The geometric configuration consists of an annular pipe attached to a cylinder.
I created the movies for pressure and axial velocity, showing their transient behavior. The movie for pressure shows that there is a spurious pressure wave bouncing between the inlet and the junction where annular pipe meets the cylinder. The movie for axial velocity shows that the flow in the annular pipe is pulsating, which I think is due to the pressure waves. Due to this pulsation, the computed mean axial velocity in OpenFOAM is far off from the experimental data.

Movies are attached here:
Pressure:
http://www.cfd-online.com/OpenFOAM_D...hment_icon.gif pres.avi
Axial velocity:
http://www.cfd-online.com/OpenFOAM_D...hment_icon.gif vel.avi

Could any body at the forum please provide me with some pointers on how to get rid of the pressure waves ? Any information would be greatly appreciated.

The BCs I used are fixed velocity, zero pressure gradient, and fixed temperature at the inlet. At the outlet, it is inletOutlet for velocity and temperature, and pressure transmissive BC for pressure.

I would me happy to provide more information on my case set-up.

Thanks!!
Regards,
Ankur

ankgupta8um February 27, 2008 21:56

Hello, Sorry.. I couldn't a
 
Hello,

Sorry.. I couldn't attach the movies as it violated the file size restrictions on the board.
Please find the movies at these links:
www.personal.psu.edu/axg330/pres.avi
www.personal.psu.edu/axg330/vel.avi

Thanks!!
Regards,
Ankur

connclark February 28, 2008 13:07

I haven't tried it and have ye
 
I haven't tried it and have yet to get a good coodles case to work, but maybe if you split the outlet patch in two and placed them at an angle to each other it would dampen the reflected wave.

ankgupta8um February 28, 2008 15:13

Hello Conn, Thanks for the
 
Hello Conn,

Thanks for the reply. The problem that I am seeing is the reflection of the pressure wave from an internal plane in the geometric configuration. The wave reflects back from the location where the annular portion meets the cylinder.
If you play the pressure movie real slow, it is clearly visible that the pressure wave moves from inlet to the location where annular pipe meets the cylinder, and then it reflects back from there.

I am getting a feeling that this pressure wave is either due to the specified BCs at the inlet, or due to the wrong choice of numerics. I did try some other BC specifications at the inlet, but that didn't help.

I would really appreciate any ideas/comments on resolving this issue of pressure waves !!

Thanks!!
Regards,
Ankur

eugene March 5, 2008 07:54

I have had this problem in the
 
I have had this problem in the past, but unfortunately have not had the opportunity to do something constructive about it. Your problem is the zeroGradient pressure boundary at the inlet. This boundary is reflective with respect to pressure waves. The interface between the annular and open sections of the domain is also partially reflective because of the large disparity in scale, so you end up with a standing wave in the annular section.

The solution: formulate and implement a non-reflecting inflow boundary. This is not as hard as it seems, as all the building blocks are available in the waveTransmissive outlet code.


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