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-   -   l Inf in wave transmissive bc (http://www.cfd-online.com/Forums/openfoam-solving/115409-l-inf-wave-transmissive-bc.html)

 VSass March 30, 2013 07:56

l Inf in wave transmissive bc

Hey guys,

does anybody know how l inf works in wave transmissive boundary condition?
In Wiki it says it's a measure of how far the farfield should be, but i don't know which exact value to give.How we difine it on each problem?

Thanks

 immortality March 30, 2013 08:28

it indicates how much of wave is reflected and how much is transferred out of the domain.you could try some values.it depends of the dimensions of your problem.if its too low it will be like totalPressure or fixedValue.set it .1 or 1 to test which is more appropriate.

 VSass April 1, 2013 04:37

Hey,

thanks for the reply. Is there anyway to precisely set the value? I mean, why to set 0.1 and not 0.3 or something else? Also, does it corresponds on a characteristic length, let's say, a diameter or a mean chord?

Regards

 immortality April 1, 2013 05:48

i think it is more a triel and error work if someone correct me.whats your problem?if you want to the waves reach the patches transfer very close to completely (maybe some numerical waves reflect) choose a large number.there are some papers i have seen about this bc in the net.
Are you certain to use this bc?why?

 VSass April 1, 2013 06:02

Well, i have compressible flow around a sphere in a spherical far field. I tried inletOutlet/outletInlet BCs for U,T,p but i didn't get the correct solution. I read somewhere that wavetransimissive bc is better for compressible unsteady problems. I'm trying to set the correct l inf in order to have an accurate solution and no reflections.

 immortality April 1, 2013 09:40

did you reach the appropriate value?let me know.also see tutorials.

 immortality April 8, 2013 15:48

did you succeed?how?with spherical or cylindrical farfield?

 VSass April 9, 2013 04:01

No success yet. If waveTransmissive is p outlet/Inlet for compressible flow, then it should work. I tried also zeroGradient for temperature, but it wasn't helpful.My flow doesn't seem to spread behind the sphere, it seems like we have reflections from the outer boundary.

 Gatoscar January 9, 2014 22:07

test

5 Attachment(s)
Quote:
 Originally Posted by VSass (Post 417500) Hey, thanks for the reply. Is there anyway to precisely set the value? I mean, why to set 0.1 and not 0.3 or something else? Also, does it corresponds on a characteristic length, let's say, a diameter or a mean chord? Regards
Hello there

I did my own tests to understand the behaviour of lInf in the waveTransmissive BC. I took the wedge example in the rhoCentralFoam solver and used Ma=2.0. Keeping everything fixed I only modified the value of lInf (the results can be seen in the attached images. The image file name is the value given i.e. plInf10e-2 means lInf=10e-2). The way I understand for values lInf>1 the far-field condition is outside of the domain, for values lInf>1 the far-field condition is inside the domain. I did tests whit values grater than 1 (lInf=10e2 and lInf=10e3), but the results were the same that lInf=10e0.

Regards

 VSass January 10, 2014 04:13

Oscar,

I agree with your results. As they show, for different lInf<1 we have a different problem each time. Truly representative work.

Regards

 immortality January 10, 2014 06:19

Quote:
 for values lInf>1 the far-field condition is inside the domain.
dear Oscar,what do you mean by being far-field inside the domain?whats the physical meaning of such situation?

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