Embodiments of an apparatus for transferring energy between a rotating element and a fluid are provided herein. In some embodiments, a plenum of an apparatus for transferring energy between a rotating element and a fluid may include a through hole disposed through the plenum; and a plurality of inlet guide vanes disposed proximate a peripheral edge of the through hole, the plurality of inlet guide vanes comprising a first group of inlet guide vanes having a cambered profile and a second group of inlet guide vanes disposed radially inward of the first group of inlet guide vanes, wherein the first group of inlet guide vanes are in a fixed position with respect to the plenum and the second group of inlet guide vanes are movable with respect to the plenum.