| Abstract: | Thrust collars (TCs) are widely used in turbomachinery such as integrally geared compressors (IGCs), gearboxes, and vehicle transmissions to transmit axial loads to a central shaft. The loading and speed capacity of TCs depends on the integrity of the lubricant film between the TC surface and the central gear surface. Lubricant cavitation and flow turbulence can adversely affect TC performance by causing instabilities and erosive damage. Accurate predictions of the oil film thickness (OFT) are necessary to identify system loads and speeds that result in the onset of cavitation/turbulence, which can lead to jeopardized TC performance. Numerous finite element (FE) and CFD models have been used to compute TC OFT and identify regions of turbulence and cavitation, but these models have yet to be validated with direct experimental measurements. The objective of this thesis research is to apply a novel in-situ optical diagnostic method, laser-induced fluorescence (LIF) imaging, to quantify the OFT in a thrust collar under realistic operating conditions. This research study includes two major components: 1) demonstrating LIF-based OFT imaging in a calibration device and identifying optimal experimental parameters, 2) performing OFT measurements in a TC under realistic operating conditions. The Texas A&M Engineering Experiment Station Turbomachinery Laboratory (TEES-TL) has developed a thrust collar test facility (TCTF) that emulates a single pinion IGC. Optical access is obtained with an acrylic TC fortified with a steel backing. A pre-determined laser dye was added to the lubricating oil to generate the laser-induced fluorescence signal from the oil film, which was detected using an intensified charge-coupled device (ICCD) camera fitted with proper optical filters. A calibration device was manufactured to quantify the LIF signal from the lubricant oil at known film thicknesses. After the proof-of-principle tests were completed, the calibration tests were repeated at the TCTF to utilize the same optics as the OFT image measurements. The TC film thickness was imaged at restricted and unrestricted flow conditions. At restricted flow conditions, the film thickness decreases with increased running speed and decreases with increased axial load, and cavitation was observed between 2000 and 2500 rpm at an axial load of 600 N. The cavitation pocket was located just above the centerline of the lubrication area, and entrance region turbulence was evident at the bottom of the lubrication area. At unrestricted flow conditions, the film thickness increases when the oil inlet speed exceeds the TC surface speed, but decreases when the TC surface speed exceeds the oil inlet speed. As turbomachinery manufacturers look to new applications requiring increased efficiency and capacity, the speed and load demands on TCs will be increased. This thesis research provides an experimental benchmark to existing FE and CFD models so that turbomachinery manufacturers can confidently extend TC capacity without compromising safe and efficient operation. The electronic version of this dissertation is accessible from https://hdl.handle.net/1969.1/198144 |
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