Windage Power Loss in Gas Foil Bearings and the Rotor-Stator Clearance of High Speed Generators Operating in High Pressure Carbon Dioxide Environments

by Robert J. Bruckner & Christopher DellaCorte
NASA Glenn Research Center

Click Here To Access The Complete Paper

Closed Supercritical Cycle (CSC) engines are prime candidates to convert heat from a reactor to electric power for robotic space exploration, habitation, and terrestrial power systems. The engine concept incorporates a motor / generator mounted on the engine shaft along with the requisite turbomachinery. Successful completion of the long duration missions currently anticipated for these engines will require designs that adequately address all losses within the machine. The preliminary thermal management concept for these engines is to use the cycle working fluid to provide the required cooling. In addition to providing the cooling the working fluid will also serve as the bearing lubricant. Losses in the gas foil bearings and within the rotor-stator gap of the generator are increasingly important as both rotational speed and mean operating pressure are increased. This paper presents the results of an experimental study that directly measured these losses at conditions up to 48 atmospheres of pressure and rotational speeds up to 42,000 revolutions per minute. A non-dimensional analysis is presented to extend the experimental results into the CSC range.