A rotor wheel for an engine includes a plurality of impeller vanes and a plurality of fluid passages defined by adjacent impeller vanes. The fluid passages are radially disposed across at least a portion of the rotor wheel. One or more impeller inserts may be disposed within one or more of the plurality of fluid passages, respectively. The impeller inserts define an impeller passage with a passage shape that controls a flow of fluid through the one or more of the plurality of fluid passages.