Browsing by Author "McLuckie, I. R. W."

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    Developments for the calculation of heavily loaded journal bearings
    (Cranfield University, 2010-05) Barrett, D. J. S.; Teixeira, Joao Amaral; McLuckie, I. R. W.
    This thesis describes the development of an ElastoHydroDynamic (EHD) bearing calculation. The effect of body forces is shown to be important for highly loaded bearings in reciprocating internal combustion engines. Extension of the program to rotating machinery includes an examination of instability in the shaft bearings of a turbocharger. The development of a parameter to predict cavitation damage in a bearing is promising. Several calculation results using the program are shown. These are engine main bearing and connecting rod big-end bearings and full floating bearings for a turbocharger. The calculations on the big-end bearing if a racing engine show why the designers were having difficulty understanding the correct location for the oil feed hole position. Effects of elastic deformation, thermal deformation and manufacturing/assembly deformation all have a significant effect on the extent of the oil film. A novel calculation for a cavitation damage parameter is demonstrated successfully for a heavily loaded diesel engine bearing. The importance of body forces on the oil film due to high accelerations on certain bearings is shown to be theoretically important but not yet demonstrated. The program was written with the intention to be incorporated into the sponsoring company’s range of engine design software. A part of that development process included carrying out calculations to demonstrate to customers and present papers at conferences. The results of some of these calculations have been included in this thesis. Results of a study on the effect of crankshaft geometry on racing engine viscous friction losses were reported in a paper presented at the IDETC conference in Long Beach, 2005. This study used the first version of the software which only included Rigid Hydro Dynamics (RHD) at the time but was usable. Results of a study on stability of shaft motion in high speed turbocharger bearings were reported in a paper at the 8th International Turbocharger conference in London, 2006. At this time the program was still only capable of RHD calculations but could now solve for multiple oil films simultaneously and sweep through the speed range. The studies on the effects of body forces and the development of a cavitation parameter will be presented in papers in the near future.
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    Instability studies of an 'O'-ring flexibly supported, gas bearing, mounted, cool air unit.
    (Cranfield University, 1990-09) McLuckie, I. R. W.; Reason, B. R.; MacFarlane, C. R.
    A Cool Air unit (C. A. U. ) is powered by air bled from the engine and supplies cool air to the avionics and cockpit of the aircraft. Essentially a small turbo machine, the rotor is mounted upon two plain (gas) air bearings, which are flexibly supported by elastomeric '0'-Rings. The project objectives were to investigate, experimentally and theoretically, the mechanism of dynamic instability, half frequency whirl (HFW) observed in the C. A. U design, and hence evaluate methods by which it can be best controlled. Two main areas of study were embarked upon. Firstly a steady state aerodynamic study, based on an existing single bearing rig, to evaluate the extent of aerodynamic operation and single bearing instability (HFW). This Test Rig did not have '0'-Ring flexibility. Bearing L/D tested were 2,1.5 and 1.0, with variable loading of 18-1 -º 51.2N and speeds of 6000 -º 40000 Rpm in approximately 5000 Rpm intervals. the theoretical study investigated non-linear effects of air film pressure distribution. Secondly a Dynamic instability study of HFW was carried out on a newly designed Test Rig, simulating small turbo machines and the C. A. U.. Three bearing types were evaluated, Aerodynamic, Hybrid and Hybrid porous. With L/D of 1.0. '0'-Ring Centres varied from 0.17 4 0-83 of bearing length. Viton and Silicon materials were tested with 70 shore hardness. Rotor mass, inertia, asymmetry and unbalance were investigated along with '0'- Ring stiffness and damping variation from air pressure (0 4 120psi). Theory was developed to determine whirl onsets and effects of unbalance, and damping of the support. Non-linear (stagnant areas) of air film detected experimentally, are not explained by Raimondi's theory. Experiments show that Raimondi's theory seriously over estimates the applicable area of fully developed aerodynamic operation. Pressure Profile at onset of Instability tends to a Sommerfeld condition. Temperature was a good indication of lubrication regime. Linear temperature rise curve denotes Aerodynamic operation, and transition to non-linear curve represents onset of Instability (HFW). Authors theory considers non-linearity of air film and suggests a new method of evaluation to improve convergence. Dynamic study of dual bearing rig concludes, first instability onset speed (RSW) can be passed through due to residual unbalance and damping in the '0'-Ring support. Theory developed shows relationship of RSW and HFW effects due to unbalance and damping and results agree well. Viton offered better damping than Silicon. RSW not present in Viton at'0'-Ring centres above 10 mm. HFW not present with Viton below 55,000 rpm. RSW observed with ui /cu = 1.0 and HFW occurred with m /m = 0-493 4 0.58. hybrid porous bearings had lower performance than hybrid, but better than aerodynamic. Hybrid bearings mounted in Viton '0'-Rings offer best performance long term. Aerodynamic bearings can be concluded to be inherently unstable and have limited aerodynamic operation, so should see little use in high speed turbo machinery, including C. A. U. or aircraft applications where zero g loading likely.