Bearings: Technology and needs
A brief status report on bearing technology and present and near-term future problems that warrant research support is presented. For rolling element bearings a material with improved fracture toughness, life data in the low Lambda region, a comprehensive failure theory verified by life data and incorporated into dynamic analyses, and an improved corrosion resistant alloy are perceived as important needs. For hydrodynamic bearings better definition of cavitation boundaries and pressure distributions for squeeze film dampers, and geometry optimization for minimum power loss in turbulent film bearings are needed. For gas film bearings, foil bearing geometries that form more nearly optimum film shapes for maximum load capacity, and more effective surface protective coatings for high temperature operation are needed.
Solid Lubricated Rolling Element Bearings
Abstract : This program deals with the development of advanced dry-lubricated bearings for cruise missile gyro and turbine engine application, keeping the latter in the focal point of the main research effort. Significant accomplishments include: (1) We established the theoretical and practical basis of and demonstrated the need for immediate bearing surface integrity studies and the need for improved, more homogeneous bearing steels. (2) In spite of the lack of experimental data, based solely on literature information and the understanding of tribology fundamentals, we were asked to predict success or failure for ion-sputtered versus chemical vapor deposited (CVD) hardcoats for high Hertzian stress, rolling element bearing use. We predicted failure of the former and sucess for the latter. Later, experimental data proved our contentions. (3) We identified reactive sputtering of selected hardcoats (e.g., titanium nitride--TiN) as the next best hardcoating process to CVD in terms of adhesion. It was further stated that reactive sputtering of selected hardcoats could be made cost effective to eliminate the overtempering problem of the CVD process and the resultant attrition due to bearing distortion.
Reduction of gas flow nonuniformity in gas turbine engines by means of gas-dynamic methods
Gas flow nonuniformity is one of the main sources of rotor blade vibrations in the gas turbine engines. Usually, the flow circumferential nonuniformity occurs near the annular frames, located in the flow channel of the engine. This leads to the increased dynamic stresses in blades and as a consequence to the blade damage. The goal of the research was to find an acceptable method of reducing the level of gas flow nonuniformity as the source of dynamic stresses in the rotor blades. Two different methods were investigated during this research. Thus, this study gives the ideas about methods of improving the flow structure in gas turbine engine. On the basis of existing conditions (under development or existing engine) it allows the selection of the most suitable method for reducing gas flow nonuniformity.