Air Bearing Development for a GM Automotive Gas Turbine

Elimination of oil from the hot section of the engine, very low running losses and potential cost reductions are incentives to develop air bearings for the high speed rotors of automotive gas turbines. Low air bearing stiffness, start-stop wear and high starting torque are design challenges in this application.

This paper outlines analytical and experimental programs undertaken by the Power Systems Department of the General Motors Research Laboratories to evaluate air bearing usage in vehicular gas turbines. Air bearing operation has been demonstrated in engine dynamometer tests. A better understanding of the many factors which affect the performance of cantilevered-leaf air bearings has been realized through extensive rotor dynamics rig testing coupled with development of bearing analysis computer programs. Measured running losses of the air bearing are much lower than those of the oil jet lubricated ball bearing it is replacing. Increasing leaf thickness, leaf-housing attachment angle, leaf free radius and eliminating the clearance between the leaf beam and housing slot increased the bearing stiffness.