A curved diffuser (210) in a gas turbine engine (201) directs a primary portion of air flow from a compressor (202) through a curved discharge opening (213) into a plenum (220). The curved diffuser (210) also comprises ports (217) through which a secondary portion of air passes into confined space (225) that is defined in part by a pressure boundary element that may be comprised of at least one plate (222) or at least one conduit (306). The at least one plate (222) and the at least one conduit (306) respectively comprise apertures (246, 312) through which pass the secondary portion of air to provide impingement-type cooling to transitions (230, 320). In various embodiments the velocity of the air between adjacent transitions (230, 320) may flow at relatively uniform velocity along the longitudinal distance of the respective transitions (230, 320).