Artur Schimpf

• The present thesis describes the experimental performance determination and numerical modeling of an aerostatic porous bearing made of an orthotropically layered ceramic composite material (CMC). The high temperature resistance, low thermal expansion and high reusability of this material makes it eminently suitable for use in highly stressed fluid-film bearing applications. The work involves the development of an aerostatic journal bearing made of porous, orthotropically layered carbon fiber-reinforced carbon composite (C/C) and the design of a journal bearing test rig, which contained additional aerostatic support bearings and six optical laser triangulation sensors. The sensor system enabled the measurement of lubricant film thickness and shaft misalignment. As a result of the slight air lubrication clearance of 30 μm, the focus was on low concentricity and the determination of shaft misalignments. The preliminary tests included the determination of the permeability of the porous material and the applicability of Darcy’s law. A scan of the inner surface of the porous bushing revealed a characteristic grooved structure, which can be attributed to the layered structure of the material. Bearing tests were conducted up to a rotational speed of 8000 rpm and a pressure ratio of 5 to 7. No significant effect of rotational speed on load-carrying capacity and gas consumption was observed in this operating range. The examined operating points did not indicate any sign of the occurrence of the pneumatic hammer. A temporary load of below 90N on the bearing and an eccentricity ratio below 0.8 did not cause any significant wear on the shaft. Four numerical models, based on Reynolds’ lubricant film equation and Darcy’s law were developed. The models were gradually extended with consideration of shaft misalignment, the compressibility of the gas, the geometry of the pressure supply chamber and the embedding of the groove structure. The models were validated with external publications and the performed tests. Numerous studies have investigated aerostatic porous bearings made of sintered metal and graphite. Current computational approaches to determine a fast preliminary design reached max. deviations of approximately 20 - 24% compared to experimental tests. One of the central claims of this research was to extend this area of investigation by porous, othotropically layered bearings made of C/C. The developed extended Full-Darcy model achieved a maximum deviation in the load-carrying capacity of 21.6% and in the gas consumption of 23.5%. This study demonstrates the applicability of a resistant material from the aerospace field (reusable thrust chambers made of CMC) for highly stressed and durable fluid-film bearings. Furthermore, a numerical model for the computation and design of these bearings was developed and validated.