a problem on Partankar's periodic boundary model
 

As what Patankar's paper proposed, the instantaneous pressure in a periodic flow is decomposed into a mean part and a fluctuating part. when the partial differential equations are solved, the mean pressure are adjusted very time step to satisfy the fixed mass flow conditions. furthermore the whole solutions are carried out by PTDMA. In partank's paper, the idea of PTDMA is very clear. but not mentiond the detailed means to achive a mean pressure. so is there some guy who can describle the procedure to determine the mean pressure. any advice will be appreciated.