Mircea D. Pascovici

A transient thermoelastohydrodynamic study of steadily loaded plain journal bearings using Finite Element Method analysis

The present paper proposes an advanced bidimensional model necessary to calculate the temperature field in a journal bearing submitted to both rapid and slow start-ups. The model takes into account realistic thermal boundary conditions at fluid film-solid interfaces. The thermoelastic deformations of both the journal and of the bush are also considered and a special attention is paid to the ruptured zone of the film. The Finite Element Method (with upwind techniques whenever necessary) is employed to solve the equations implied by the model. Finally, the theoretical predictions were validated by comparison with experimental data.

On the Scuffing Failure of Hydrodynamic Bearings in the Presence of an Abrasive Contaminant

The presence of rigid particulate contamination in hydrodynamic bearings is known to lead to considerable damage resulting in failure. This paper presents a model for evaluating the flash temperature between a fixed, rigid particle embedded into the bearing over-layer while in contact with the slider. Scuffing is assumed to occur if the flash temperature exceeds a certain critical value. The model provides a convenient procedure for estimating an appropriate filter size. Examples are provided to illustrate the utility of the model.

Thermoelastohydrodynamic (TEHD) Analysis of a Grooved Thrust Washer

A numerical model is developed to analyze the influence of thermal deformations on the performance of a radially grooved thrust washer. The analysis couples the flow phenomena (including cavitation) in the lubricant with the heat transfer in both the fluid and solid media, as well as with the thermally induced deformations in the solid parts. The finite element method (both two-dimensional and three-dimensional, with linear and quadratic shape functions) is used to solve the Reynolds equation for flow, the energy equation for temperature and the thermo-elasticity equations for deformations in the solid. Grid coupling is achieved by using a Newton-Raphson iteration. Realistic boundary conditions and geometry are used for the fluid and solid domains. The results show that, for the case of a properly shaped stator the thermal deformations can lead to an increase in bearing performance.

Pressure and Temperature Field Measurements of a Lightly Loaded Circumferential Groove Journal Bearing

The current study presents the experimental determination of the lubricant film pressure and temperature distributions on one land of a symmetrical two-land circumferential groove journal bearing (CGJB) operating under low-load steady-state conditions. Film pressure and temperature measurements are done both in axial and circumferential directions. Five axial planes, with three equally spaced pressure tappings per plane, construct the base pressure measurements grid. The pressure tappings circumferential location is shifted 20° from one plane to the neighboring plane. Similarly, the base temperature measurements grid consists of four axial planes, with three equally spaced thermocouples per plane. Hence, by rotating the bearing sequentially, with an angular step of 10°, it is possible to create fine measurement grids. This method of measurement is valid, because the circumferential groove journal bearings operation is independent on the angle of loading. Two supply pressures were considered for the tests. The higher supply pressure leads to a smoother bearing operation. In the diverging zone, subatmospheric regions were measured. Superposing pressure and temperature fields reveals that the maximum temperatures are encountered in the sharp pressure drop region.

Study of a Novel Squeeze Film Damper and Vibration Generator

A novel squeeze film damper and vibration generator (SFD&VG) is proposed as an option in the vibration control field. The SFD& VG can be used as an active squeeze film damper (ASFD) or as a vibration generator (vibrator), for unidimensional vibration damping or generation. The SFD&VG concept is connected with current research to improve a common industrial process-drilling of deep holes. The SFD&VG is based on the variable area of the lubricant film, which allows the development of a variable force, and a change in fluid film stiffness and damping. The analysis is initiated for an elementary configuration of the SFD&VG-the infinite width Rayleigh step case-and then it is developed for an advanced elliptical SFD&VG. The Reynolds equation is solved for both pure squeeze film effect which provides vibration damping, and pure hydrodynamic wedge effect which provides vibration generation. The the oretical part is continued with the SFD&VG dynamic simulation. The SFD&VG experimental device and vibration measurements, performed for the two defined regimes, ASFD and vibration generator, are presented. Finally, the experimental and theoretical results are briefly compared.

Analysis of a Torsional Fluid Film Vibrator

A novel hydrodynamic system, called torsional fluid film vibrator (TFFV) is proposed. This device is complementary to the Lanchesters absorber and presents a classical response of a one-degree of freedom linear system with a periodical self-excitation. The fluid film thickness variation produces a variable viscous drag moment, which drives the elastically supported bush in a torsional oscillatory movement. The TFFV concept is connected with current research to improve the drilling technology of deep holes. The Navier-Stokes equations are solved on the particular geometry of this vibrator and the viscous drag moment is explicitly presented. The theoretical part is continued with the TFFV dynamic simulation and the analysis of the influence of the geometrical parameters on the amplitude of the viscous drag moment. Computed structural friction power and the amplitude of vibration agree reasonably well with the experimental measurements conducted on a TFFV test rig.

Transient Pressure and Temperature Field Measurements in a Lightly Loaded Circumferential Groove Journal Bearing from Startup to Steady-State Thermal Stabilization

ABSTRACT The fluid film pressure and temperature fields have been measured simultaneously under laboratory conditions at one land of a circumferential groove journal bearing (CGJB), together with friction torque and oil flow rate, during a time span from stand-still startup to the development of a thermally stabilized steady operating regime.A very fine measurement grid—that is, 216 pressure and 180 temperature points spread across the axial and circumferential directions—has been obtained by joining and synchronizing measurements from separate test runs while rigorously re-creating the test conditions.The study confirmed that the pressure field is established faster than the temperature field, that film rupture occurs both from cavitation nuclei downstream the minimum film thickness and through air ingestion from the environment. Furthermore, the high pressures in the convergent zone stabilize relatively quickly, whereas the low pressures in the divergent zone cavitated region require a longer time to stabilize. The cavitated region reverse flow appearance has been identified thermally through upstream-oriented isotherms. This study is the first to present the transient evolutions of pressure and temperature fields.

Squeeze processes in a narrow circular damper with highly compressible porous layer imbibed with liquids

Squeeze film dampers are widely used technical components for turbomachinery as a means to reduce the amplitude of rotor vibration owing to unbalance. This article proposes a different type of circular damper using highly compressible porous layers (HCPL) imbibed with Newtonian liquids. The elastic forces of the HCPL solid phase are negligible compared to the hydrodynamic forces generated within the porous layer. Such processes were named ex-poro-hydrodynamic (XPHD). The Kozeny–Carman equation was used to compute permeability in function of porosity/compacticity. Analytical and numerical solutions were performed for the impact process of the partial and full narrow circular dampers in XPHD conditions. The results were compared with the case of the classical squeeze film damper. The damping capacity of a HCPL imbibed with Newtonian liquid was found to be considerably greater than that of the Newtonian liquid layer.