Abstract: A compressor includes a diffuser, a recirculation duct, and a flow control valve. The recirculation duct has an inlet in fluid communication with the air outlet of the diffuser, and an outlet in fluid communication with the air inlet of the diffuser. The flow control valve is selectively moveable between open and closed positions, to thereby fluidly couple and isolate, respectively, the recirculation duct inlet and outlets. During operation of the compressor, the flow control valve may be opened, which circulates a portion of the compressed air discharged from the diffuser air outlet back to the diffuser air inlet. The air that is circulated back to the diffuser air inlet reduces the effective area of the diffuser air inlet, thereby increasing the surge margin of the compressor.

Abstract: A compressor includes an enhanced vaned shroud and is configured such that the flow area ratio is equivalent to that of a conventional, non-vaned shroud. The vaned shroud includes a plurality of airfoils that vary in thickness to obtain desired vibrational mode shapes and natural frequencies. A stiffening ring of limited axial extent is coupled to, and between, the airfoils, and the shroud is manufactured with a section of constant radius.