No description available.

The design of advanced, state-of-the-art turbomachinery requires accurate analytical tools for predicting rotor response and evaluating stability. One of the required tools is a reliable analytical code for predicting the performance of fluid-film bearings. This work presents an initial evaluation of a test rig for verifying such codes. This presentation includes background information on the techniques and terminology of fluid-film bearing analysis and two basic approaches to experimental evaluation of fluid-film bearings. To establish one such code, NPADVT, as a useful tool for evaluating the performance of the test rig, comparisons between six published, experimental evaluations of fluid-film bearings for static characteristics and the corresponding NPADVT analysis are presented. With the code thus anchored, and its limits established, experimental data generated with the test rig are compared to appropriate analyses and the test rig shown to be essentially functional. Finally, experimental static results for a pocket bearing generated with the test rig are presented and compared with analysis. / Master of Science

Rotor stability is essential to the life span of any piece of rotating machinery; it becomes increasingly critical in high-speed machinery such as turbochargers. Large turbochargers, such as those found in marine diesel propulsion engines where the rotor alone often exceeds forty pounds, require careful consideration regarding stability as well as load support during the bearing selection process. Logarithmic Decrement is the primary consideration for rotor stability. Commercial software is used to model and analyze a proven unstable turbocharger rotor. After confirming that the model exhibits unstable characteristics, the same turbocharger is then analyzed with various fluid-film bearing configurations. Finally, the tilting-pad bearing is determined to be the best bearing for this turbocharger application, stabilizing the rotor throughout the entire designed operating range. / Master of Science

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.

With increasing rotor flexibility and shaft speeds, turbomachinery undergoes large dynamic loads and displacements. Squeeze film dampers (SFDs) are a type of fluid film bearing used in rotating machinery to attenuate rotor vibration, provide mechanical isolation, and/or to tune the placement of system critical speeds. Industry has a keen interest in designing SFDs that are small, lightweight, and mechanically simple. To achieve this, one must have a full understanding of how various design features affect the SFD forced performance. This thesis presents a comprehensive analysis, experimental and theoretical, of a short (L=25.4 mm) open ends SFD design incorporating three lubricant feed holes (without a circumferential feed groove). The damper radial clearance (c=127 μm), L/D ratio (0.2), and lubricant (ISO VG2) have similar dimensions and properties as in actual SFDs for aircraft engine applications. The work presents the identification of experimental force coefficients (K, C, M) from a 2-DOF system model for circular and elliptical orbit tests over the frequency range ω=10-250Hz. The whirl amplitudes range from r=0.05c-0.6c, while the static eccentricity ranges from eS=0-0.5c. Analysis of the measured film land pressures evidence that the deep end grooves (provisions for installation of end seals) contribute to the generation of dynamic pressures in an almost purely inertial fashion. Film land dynamic pressures show both viscous and inertial effects. Experimental pressure traces show the occurrence of significant air ingestion for orbits with amplitudes r>0.4c, and lubricant vapor cavitation when pressures drop to the lubricant saturation pressure (PSAT~0 bar). Identified force coefficients show the damper configuration offers direct damping coefficients that are more sensitive to increases in static eccentricity (eS) than to increases in amplitude of whirl (r). On the other hand, SFD inertia coefficients are more sensitive to increases in the amplitude of whirl than to increases in static eccentricity. For small amplitude motions, the added or virtual mass of the damper is as large as 27% of the bearing cartridge mass (MBC=15.15 kg). The identified force coefficients are shown to be insensitive to the orbit type (circular or elliptical) and the number of open feed holes (3, 2, or 1). Comparisons of damping coefficients between a damper employing a circumferential feed groove1 and the current damper employing feed holes (no groove), show that both dampers offer similar damping coefficients, irrespective of the orbit amplitude or static eccentricity. On the other hand, the grooved damper shows much larger inertia force coefficients, at least ~60% more. Predictions from a physics based model agree well with the experimental damping coefficients, however for large orbit motion, over predict inertia coefficients due to the model neglecting convective inertia effects. Credence is given to the validity of the linearized force coefficients by comparing the actual dissipated energy to the estimated dissipated energy derived from the identified force coefficients. The percent difference is below 25% for all test conditions, and in fact is shown to be less than 5% for certain combinations of orbit amplitude (r), static eccentricity (eS), and whirl frequency (ω).

No description available.

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.

No description available.

This project was initiated to more fully understand the dynamic stability of an automotive turbocharger rotor-bearing system using both linear and nonlinear analyses. The capabilities of a commercial Finite Element Analysis (FEA) code (computer program) were implemented in the investigation process. Several different hydrodynamic journal bearings were employed in the study of the turbocharger linearized dynamic stability. The research demonstrates how the linear analysis of a turbocharger rotordynamics can be very beneficial for the design evaluation and maintenance purposes. / Master of Science

"Two most important events in the history of lubrication theory are attributed to Reynolds and Sommerfeld. Reynolds derived the governing equations for lubricating films in simplifying the Navier-Stokes equations considering thin-film effects. Sommerfeld obtained a closed form analytical solution to the Reynolds equation for the long bearing (one-dimensional case) with fixed constant eccentricity which results in a point symmetric pressure profile compared to an arbitrary (ambient) level. In attempting to reconcile with experimental evidence, Gumbel advanced the argument that sub-ambient pressure in a fluid film is not possible. On the basis that the fluid film would rupture, he put forth that the sub-ambient portion of the Sommerfeld solution should be discarded, a proposition that is commonly recognized as the half-Sommerfeld solution (of Gumbel). Ever since Gumbel suggested this improvement, much interest remains regarding the physical process of rupture in bearing lubricating films. In lubrication literature, cavitation is used interchangeably with rupture to indicate a condition in which an abundance of a gas phase, essentially ambient air, is present in a portion of the bearing clearance. A cogent two-phase morphology for addressing cavitation in long bearings is postulated in order to predict time-dependent fluid behavior from an initial state that is a generalization of Gumbel’s half-Sommerfeld solution. The ultimate steady-state is presumed to satisfy the hypothesis of Swift and Stieber that an ambient condition is reached by the rupture point at an unspecified location simultaneously with a vanishing pressure gradient. A trans-rupture continuity equation, as proposed by Olsson, determines a formula for the speed of a moving rupture point requiring a specific model of the two-phase flow in the rupture region. Employing an adhered film model, sequential application of Olsson’s equation to the rupture points of the intermediate states between the half-Sommerfeld and Swift-Stieber states renders an interpretation of a time-dependent progression towards a steady-state solution. Closed form analytical formulas, which readily combine to provide an exact solution to the Reynolds equation are derived with the start (formation point) of the full-film other than the customary bearing maximum gap and with the rupture point at any assigned intermediate location. Each valid solution for an intermediate state yields an invariant flux that must satisfy a window of constraints to exclude the possibility of sub-ambient pressures. A complete set of such valid solutions exists for each fixed eccentricity and can be depicted as a contour plot of the invariant flux with formation and rupture points as coordinates. The method can readily be extended to two-dimensions, offering a promising alternative to the Elrod cavitation algorithm, which is commonly used in more comprehensive bearing analyses."