An additive manufacturing (AM) apparatus is provided, having a build unit including a powder delivery mechanism, a powder recoating mechanism, and an irradiation beam directing mechanism. The AM apparatus further includes a rotatable build platform having an inner diameter and an outer diameter. A fluid flow mechanism includes an inlet body forming an inlet plenum and a collector body extended from the inlet body. The collector body forms a collector plenum in fluid communication with the inlet plenum. The collector body forms an outlet opening, wherein the outlet opening is positioned proximate to the inner diameter of the rotatable build platform. The outlet opening is configured to provide a flow of fluid toward the outer diameter above the rotatable build platform.