replacing of shock tube high pressure part with a boundary condition for low pressure
 

I simulated a case of shock tube with high pressure part of 932190pa and low pressure part of 303975pa.I found that during the run pressure in mid places is around 600000pa and total pressure about 650000.
now I want to only simulate low pressure part and need to replace high pressure part by an appropriate boundary condition.
then which pressure should I put there in the patch in return of high pressure part for pressure?
932190pa that is the value of high pressure part in first time or 650000 as total pressure?
which seems more correct?:confused:
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