An apparatus for translating motive energy includes a rotor structure, having mutually spaced rotor members, adapted to react with fluids within the housing. In one embodiment, the rotor structure is rotationally driven by an external power plant for pumping fluids through a tangentially oriented outlet duct. In a second embodiment, the apparatus is driven by fluid under pressure which is conducted toward the rotor structure through an inlet aligned with peripheral portions of the rotor members, for rotationally driving the rotor structure. A variable geometry inlet control system is provided for controlling fluid flow in response to varying flow conditions and for directioning fluid flow to a portion of the rotor structure. The apparatus incorporates a structural configuration which permits its construction of carbonized composite materials, for operation at elevated temperatures.