# characteristic boundary conditions

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 April 25, 2013, 08:03 characteristic boundary conditions #1 New Member   Join Date: Apr 2013 Posts: 15 Rep Power: 6 Sponsored Links Hi all, I would like to make sure if I get the idea right about the characteristic boundary conditions. Say, in the case of the inflow being subsonic and the outflow being supersonic, how many boundary conditions I have to impose? The flow is 3D. I guess the answer is that since the goal is to zero the inflow characteristics, I have to impose two boundary conditions at the inlet (for u+a and u characteristics) and do nothing for the outlet. Is this correct? What if in this case, I set all the inflow to zero? Will this generate any spurious waves? Best, Shu

April 25, 2013, 10:14
#2
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Filippo Maria Denaro
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Quote:
 Originally Posted by shubiaohewan Hi all, I would like to make sure if I get the idea right about the characteristic boundary conditions. Say, in the case of the inflow being subsonic and the outflow being supersonic, how many boundary conditions I have to impose? The flow is 3D. I guess the answer is that since the goal is to zero the inflow characteristics, I have to impose two boundary conditions at the inlet (for u+a and u characteristics) and do nothing for the outlet. Is this correct? What if in this case, I set all the inflow to zero? Will this generate any spurious waves? Best, Shu
you are right, however I do not understand what do you mean for "the goal is to zero the inflow characteristics"

April 26, 2013, 11:01
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 Originally Posted by FMDenaro you are right, however I do not understand what do you mean for "the goal is to zero the inflow characteristics"
Hi,

To zero the characteristics means we don't want any reflection occurring at the boundary, so the boundary condition will mimic an infinite boundary condition.

Shu

April 26, 2013, 11:30
#4
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Filippo Maria Denaro
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 Originally Posted by shubiaohewan Hi, To zero the characteristics means we don't want any reflection occurring at the boundary, so the boundary condition will mimic an infinite boundary condition. Shu

ok, however as I know the correctness of the bc.s setting for subsonic/supersonic flows is not sufficient to avoid reflection but it depends on further issues. As an example, this old paper illustrated some cases http://www.sciencedirect.com/science...21999192900462.
Of course, many other recent papers were published

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