Is it possible to specify a pressure boundary in star cd that permits only inflow into the domain. Please remember that the quantity of inflow is an unknown parameter. Thanks in advance

If you know your stagnation pressure rather than you static pressure then you could use a stagnation boundary: this only allows inflow. Otherwise you would have to use a pressure boundary with your known static pressure; the flow will decide for itself whether there is inflow or outflow or both.

Do you have a compressible flow and pressure boundary used at the 'outlet'? If yes, there is a possibility that you may have recirculation at the pressure boundary, i.e. flow coming in through the outlet boundary. Do read the article on compressible flow on adapco-online.com. It will clear all your doubts. Ashish