This thesis evaluates the application of Reynolds equation in calculating fluid film forces (FFFs) in circumferential groove journal bearings (CGJBs) with both balanced and unbalanced rotors. The existing rig was fabricated at UNSW for that purpose. Unfortunately the rig was unsuitable because it was unstable at speeds as low as 500 rpm. This occurred because, when designing the rig, the traditional ??-film cavitation boundary model (CBM) was used. Consequently a modified cavitation boundary model (MCBM) was proposed which correctly predicted the instability threshold of the rig. Using the MCBM, new bearings were installed and the modified rig was stable in the required speed range up to 2400 rpm. Two existing computer programs to calculate bearing stiffness and damping coefficients and FFFs were modified for the purposes of this study. In addition, only dynamic components (AC components) of experimental FFFs could be measured accurately. The vertical mean value (DC component) of experimental FFF was approximated to the vertical reaction force and the horizontal DC component of experimental FFF was approximated to zero at each bearing. This thesis concludes that the numerical solution of Reynolds equation to calculate DC components of FFFs in a CGJB is valid with a proper selection of CBM. The agreement of AC components of the FFFs were good with a balanced rotor, but were poor with an unbalanced rotor. The modified CBM is more accurate than the existing ??-film CBMs. The cavity region is important to obtain accurate numerical results and depends on test conditions, bearing dimensions, etc. To design for critical speeds, cavitation pressure could be either oil vapour pressure or atmospheric pressure; however, to design for stability, cavitation pressure should be oil vapour pressure, or even much lower. Two halves of a CGJB carried different loads because of misalignment and different clearances. In addition, reducing length and increasing clearance significantly increased the stability of the rig. Finally, to obtain perfect agreement between numerical and experimental FFFs, short bearings and a smaller clearance ratio are strongly recommended. A special design to measure cavitation pressure is suggested.
| Identifer | oai:union.ndltd.org:ADTP/242688 |
| Date | January 2007 |
| Creators | Pham, Anh Duc, Mechanical & Manufacturing Engineering, Faculty of Engineering, UNSW |
| Publisher | Awarded by:University of New South Wales. School of Mechanical and Manufacturing Engineering |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | Copyright Anh Duc Pham, http://unsworks.unsw.edu.au/copyright |
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