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A numerical method is used to predict flow fields and forces for squeeze film dampers (SFDs). A two dimensional SFD is modeled with different amplitudes and frequencies of the journal orbiting inside the wall. In addition to the typical circular centered orbit (CCO) motion prescribed in most studies, orbits can vary greatly from circular to linear. The study is divided into two distinctive models including single phase flow model and two phase flow model. The single phase flow model cases including three amplitudes, i.e. 0.002, 0.001, and 0.0005 inches, and three frequencies, i.e. 10, 50, and 200 Hz, of journal motions are conducted to portray flow fields and forces and ultimately determine their relationships. The numerical prediction shows that the journal amplitude and frequency affect flow and consequently force in the SFD. The force is directly proportional to frequency and motion amplitude. Owing to the presence of cavitation in the practical SFD, the two phase flow model is also presented with the journal amplitude of 0.0002 and three frequencies of 10, 50, and 100 Hz, respectively. The ambient pressure condition was set up for numerical processing ranging from 0.001 Mpa to 100 Mpa. The results indicate that the operating pressure has an integral role in suppressing the presence of the cavitation. The caviation disappears if the operating pressure is high enough above the vapor pressure of the lubricant.

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).

<p>The objectives of this investigation were to experimentally and numerically assess the performance of a ball bearing supported turbocharger (TC). Turbochargers are mechanical devices used to improve the efficiency of modern engines. Using ball bearings improves the TC efficiency, and represents one of many evolving high-speed applications for ball bearings.</p> <p>The experimental objectives of this investigation were to design and develop a turbocharger test rig (TTR) to measure the shaft whirl of the rotating assembly and the axial and frictional loads experienced by the bearing cartridge. The TTR contains a ball bearing TC which was instrumented and operated under a variety of test conditions including rotational speeds up to 55,000 rpm. In order to measure the axial loads on the compressor and turbine sides, customized sensors were designed, fabricated and integrated into the TC housing. The anti-rotation (AR) pin, which normally prevents the bearing cartridge from rotating, was replaced with a custom-made sensor to measure frictional losses in the bearing cartridge.  These sensors were designed to minimally affect the operation of the TC. Proximity probes were initially installed on the compressor side and later on the turbine side to monitor shaft whirl using targets attached to the ends of the impellers. An assembly to record axial shaft motion with a proximity probe was also developed. Axial load and motion results indicated that the compressor side bears most of the axial load. As the backpressure or the speed of the TC increased the axial load also increased. Frictional measurements from the AR pin sensor demonstrated low power losses in the ball bearing cartridge. For certain shaft speed ranges, the data from the sensors illustrated periodic trends in response to subsynchronous whirl of the shaft.</p> <p>The numerical modeling objectives of this investigation were to characterize the dynamics of the ball bearing supported TC. In this TC, the compressor, turbine and shaft are supported by a bearing cartridge composed of back-to-back angular contact ball bearings. The cartridge is supported by squeeze film dampers (SFDs) and is prevented from rotation by the AR pin. To achieve the objectives, first an equivalent bearing model was developed to investigate the bearing dynamics and whirl of the TC rotating assembly. The TC bearing cartridge was modeled with a single deep groove ball bearing (DGBB) using the discrete element method. The SFD which supports the bearing was modeled with a bilinear spring and damper. A DGBB was used because it can support axial load in both directions. This model was then extended to include a flexible shaft represented by tetrahedral finite elements and supported by an ACBB cartridge. After this model was used to reproduce the whirl from the test rig, the bearing internal geometry and SFD properties were adjusted to determine their effect on shaft whirl. Wear and damage criteria were also developed to evaluate the simulation results. The best simulation result was obtained with a small clearance in the bearing and with a stiffer SFD. The clearance was necessary as the shaft and bearing deform at high speeds, preloading the bearing.</p> <p>The best simulation result was found to have reduced sliding and limited variation in contact force, which should lead to reduced friction and improved overall life. This study demonstrates the importance of taking the bearing system into account while designing a TC or other high speed mechanical system, as the bearing and SFD properties can have a significant impact on the system performance.</p>