A method of designing a gas turbine engine includes locating purge openings in fluid communication with a first stage cavity. At least one of a cover plate or a rotor disk is positioned adjacent the first stage cavity and radially inward from the purge openings. A portion of a rotor blade is positioned radially outward from the purge openings. A mass flow rate of cooling air through the purge openings is selected based on a radial location of the purge openings to create an air barrier between a radially inner side of the purge openings and a radially outer side of the purge openings.