Minel J. Braun

An Experimental Investigation of the Vaporous/Gaseous Cavity Characteristics of an Eccentric Journal Bearing

This paper describes the experimental pressure and temperature results obtained when rotating a shaft in an eccentric lucite casing at velocities raging from 209 to 628 rad/s (2000 to 6000 rpm). The results are presented in terms of three-dimensional plots and contour maps. Photographic evidence is presented to illustrate how the downstream and upstream regions of the cavity develop and evolve into the well-known finger patterns. A comparison between pressure and temperature profiles in air-saturated oil and carbon dioxide-saturated oil is presented; the origin and nature of the gases contained in the cavity are discussed. Three analytical models (Swift-Stieber, separation, Floberg) predicting the formation of the cavitation zone are presented and evaluated in light of the experimental results. A motion-picture supplement depicting these results is available upon request. Presented as an American Society of Lubrication Engineers paper at the ASME/ASLE Lubrication Conference in Washington, D.C., October 5–...

Numerical and Analytical Study of Fluid Dynamic Forces in Seals and Bearings

A numerical model based on a transformed, conservative form of the three-dimensional Navier-Stokes equations and an analytical model based on “lumped” fluid parameters are presented and compared with studies of modeled rotor/bearing/seal systems. The rotor destabilizing factors are related to the rotative character of the flow field. It is shown that these destabilizing factors can be reduced through a descrease in the fluid average circumferential velocity. However, the rotative character of the flow field is a complex three-dimensional system with bifurcated secondary flow patterns that significantly alter the fluid circumferential velocity. By transforming the Navier-Stokes equations to those for a rotating observer and using the numerical code PHOENICS-84 with a nonorthogonal body fitted grid, several numerical experiments were carried out to demonstrate the character of this complex flow field. In general, fluid injection and/or preswirl of the flow field opposing the shaft rotation significantly intensified these secondary recirculation zones and thus reduced the average circumferential velocity, while injection or preswirl in the direction of rotation significantly weakened these zones. A decrease in average circumferential velocity was related to an increase in the strength of the recirculation zones and thereby promoted stability. The influence of the axial flow was analyzed. The lumped model of fluid dynamic force based on the average circumferential velocity ratio (as opposed to the bearing/seal coefficient model) well described the obtained results for relatively large but limited ranges of parameters. This lumped model is extremely useful in rotor/bearing/seal system dynamic analysis and should be widely recommended. Fluid dynamic forces and leakage rates were calculated and compared with seal data where the working fluid was bromotrifluoromethane (CBrF3 ). The radial and tangential force predictions were in reasonable agreement with selected experimental data. Nonsynchronous perturbation provided meaningful information for system lumped parameter identification from numerical experiment data.

A bulk flow model of a brush seal system

Fibers can be readily fabricated into a variety of seal configurations that are compliant and responsive to high speed or lightly loaded systems. A linear, circular, or contoured brush seal system is a contact seal consisting of the bristle pattern and hardened interface. When compared to a labyrinth seal, the brush seal system is superior and features low leakage, dynamic stability, and permits compliant structures. But in turn, the system usually requires a hardened smooth interface and permits only limited pressure drops. Wear life and wear debris for operations with static or dynamic excitation are largely undetermined. A seal system involves control of fluid within specific boundaries. The brush and rub ring (or rub surface) form a seal system. Design similitudes, a bulk flow model, and rub ring (interface) coatings are discussed. The bulk flow model calculations are based on flows in porous media and filters. The coatings work is based on experience and expanded to include current practice.

Simulation and Control of an Active Tilting-Pad Journal Bearing

This study developed an active tilting-pad journal bearing with a feedback control system to regulate the orbit of a rotating shaft. The control is implemented by means of linear actuators installed behind the pivot of each pad, which allow the radial motion of the pads in real time. The control design uses the linear feedback of the state variables of the bearing-rotor system, with the feedback gains determined by the optimization of a quadratic performance index. The optimization is based on a linear spring-mass model that incorporates the direct stiffness and damping elements associated with each of the bearing pads. This linear model is found by the simulation of the system under small perturbations using a nonlinear Reynolds equation model. The nonlinear model is capable of simulating the radial motions of the pads by the actuators and is used to verify the effectiveness of the feedback control. It is shown that certain design parameters in the quadratic performance index may be used to determine both the stiffness and the damping of the closed-loop bearing system and that the shaft orbit can be thereby suitably regulated.

Flow visualization and quantitative velocity and pressure measurements in simulated single and double brush seals

The brush seal configuration was tested in a gravity fed water tunnel and a pump driven pressurized oil tunnel. Visualization of the flow field revealed regions that are characteristically river jetting, vortical, crossflow and exist upstream, downstream or within the seal

Flow Visualization in a Simulated Brush Seal

A method to visualize and characterize the complex flow fields in simulated brush seals is presented. The brush seal configuration was tested in a water and then in an oil tunnel. The visualization procedure revealed typical regions that are rivering, jetting, vortical or lateral flows and exist upstream, downstream or within the seal. Such flows are engendered by variations in fiber void that are spatial and temporal and affect changes in seal leakage and stability.While the effects of interface motion for linear or cylindrical configurations have not been considered herein, it is believed that the observed flow fields characterize flow phenomenology in both circular and linear brush seals. The axial pressure profiles upstream, across and downstream of the brush in the oil tunnel have been measured under a variety of inlet pressure conditions and the ensuing pressure maps are presented and discussed.Copyright

Gear Fault Detection with Time-Frequency Based Parameter NP4

The fact that the Wigner-Ville Distribution (WVD) can represent the energy of a gear vibration signal was used for the gear damage detection. A new gear fault detection parameter called NP4 is derived from the joint timefrequency Wigner-Ville Distribution. The novelty of the NP4 parameter is in application of the previously de®ned statistical parameter called kurtosis to the WVD data and its interpretation for gear fault detection. The important distinct feature of the fault detection parameter NP4 from other fault detection parameters, such as ®gures of merit, is that it does not compare a measured gear vibration signal with the ideal one. Thus, the parameter NP4 can work for the fault detection without a long recorded vibration history of the gear. New techniques for enhancing the information content of the WVD of the gear vibration signal and the reliability of the parameter NP4 are also described. The utility of the gear fault detection parameter has been demonstrated using numerous gear vibration experiments. A correlation between the level of the gear tooth damage and the value of the gear fault detection parameter NP4 is demonstrated. The gear fault detection strategy based on the developed parameter NP4 is presented and investigated in the paper.

New Gear-Fault-Detection Parameter by Use of Joint Time-Frequency Distribution

Anewgear-fault-detectionparametercalledNP4 isintroduced.Thisfault-detectionparameterutilizestheproperties of the joint time ‐frequency analysis given by the Wigner ‐Ville distribution (WVD) and kurtosis. With the WVD, the instantaneous power of the gear-vibration signature for one complete rotor revolution can be obtained. The presence of single-gear-tooth damage can be manifested by the existence of an instantaneous power distribution with a peakedness larger than the normal distribution. The normalized kurtosis, a fourth-order statistical parameter calculated for the instantaneous power distribution, provides the gear-fault-detection parameter NP4. The developed fault-detection parameter NP4 is sensitive to gear-tooth damage, especially for damage in a single tooth. The application of this NP4 fault-detection parameter was demonstrated by experimental data obtained from a gear test rig. The results showed that the NP4 parameter, used with the WVD, can provide an accurate fault identie cation of gear-tooth damage. The parameter NP4 would be of help to the practitioners in the e eld of machine health monitoring.

The Friction Behavior of Individual Components of a Spark-Ignition Engine During Warm-Up

The research presented herein fills a void in the published literature through investigation of transient friction contributions by individual internal combustion engine components during simulated engine warm-up. Currently, engine manufacturers design internal combustion engines primarily for use at steady-state operating conditions with little design consideration for transient engine warm-up. Using the motoring torque waveform and cycle-averaged data of a spark-ignition internal combustion engine, the present work determined the friction behavior of individual engine component assemblies, including the valve train, pistons and connecting rods, oil pump, and crankshaft of a modern internal combustion engine. A common criticism of the standard motoring method is that the engine does not warm up, so lubricant temperature and viscosity does not model that of a fired engine. In the present study, the lubricant and coolant were warmed from 25 to 85°C. Observations were presented as to the effect of engine speed and the temperature of the coolant and lubricant on total engine friction. Contributions of individual engine components to total engine losses were examined, as well as their variation with engine temperature. The added knowledge of the transient effects of engine temperature can help future designers to mitigate friction and component wear, thus improving overall maintenance costs, specific fuel consumption, and emissions. Presented at the STLE Annual Meeting in Las Vegas, Nevada May 15-19, 2005 Review led by Gary Barber

Two- and Three-Dimensional Numerical Experiments Representing Two Limiting Cases of an In-Line Pair of Finger Seal Components

The work presented here concerns the numerical development and simulation of the flow, pressure patterns, and motion of a pair of fingers arranged one behind the other and axially aligned in line. The fingers represent the basic elemental component of a finger seal and form a tight seal around the rotor. Yet their flexibility allows compliance with rotor motion and, in a passive-adaptive mode, compliance with the hydrodynamic forces induced by the flowing fluid. Although this article does not treat the actual staggered configuration of a finger seal, the in-line arrangement represents a first step toward that final goal. The numerical two-dimensional (axial-radial) and three-dimensional results presented herein were obtained using a commercial package (CFD-ACE+). Both models use an integrated numerical approach, which couples the hydrodynamic fluid model based on Navier-Stokes equations to the solid mechanics code that models the compliance of the fingers.