Azzedine Dadouche

Performance of a Hydrodynamic Fixed Geometry Thrust Bearing: Comparison between Experimental Data and Numerical Results

The objective of this study is to analyze the performance of a hydrodynamic thrust bearing with eight fixed pads. A comparison between experimental data and numerical results obtained by a thermohydrodynamic model is presented. The influence of the oil supply temperature, the applied load, and the rotational speed on the thrust bearing performance characteristics such as temperature field, minimum film thickness, leakage flow, and power loss is analyzed and discussed. The agreement between the experimental and numerical results is generally satisfactory.

Numerical Study of the Sensitivity of Tilting Pad Journal Bearing Performance Characteristics to Manufacturing Tolerances: Steady-State Analysis

The bearing selection for rotating machinery is based on predictions obtained for nominal dimensions. Very often the experienced performance is different than that expected. In this paper the authors theoretically analyze the possible effects of deviations from the nominal parameters of tilting-pad journal bearings on their operating characteristics. Using an example of five-pad tilting-pad journal bearings, the effects of realistic variations of pad and bearing clearances, pivot angular position, and pad angular extent have been evaluated theoretically for bearings with different diameters and L/D ratios. The characteristics analyzed in this study include operating temperatures, friction loss, minimum film thickness, and pressure.

A Comparison Study Between Acoustic Sensors for Bearing Fault Detection Under Different Speed and Load Using a Variety of Signal Processing Techniques

The use of ultrasonic sensor technology to detect incipient and evolving defects in rotating components such as bearings and gears is more desirable due to their high resolution. In a previous study, the sensitivity of a variety of sensors including an air-coupled ultrasound transducer to bearing faults was analyzed and thoroughly discussed. This article investigates the effectiveness of two ultrasonic sensors, namely, air-coupled and piezoelectric ultrasound transducers for rolling element bearings damage diagnostics. The former is a noncontact sensor and the latter is a contact sensor. An accelerometer was also used as the baseline sensor for comparison purposes. A series of tests was carried out on a laboratory test rig running with defective and undamaged healthy bearings under variable shaft speeds and several radial loads. The data were analyzed using selected signal processing techniques covering time, frequency, and advanced joint time–frequency domains. The results showed that certain acoustic features were responsive to the variation of operational condition and the damage; the detection capability of the sensors varied depending on the defect size, its location, as well as the applied signal analysis technique.

Tribological Characterization of Plasma-Sprayed CoNiCrAlY-BN Abradable Coatings

The processing conditions, microstructural and tribological characterizations of plasma-sprayed CoNiCrAlY-BN high temperature abradable coatings are reported in this manuscript. Plasma spray torch parameters were varied to produce a set of abradable coatings exhibiting a broad range of porosity levels (34-62%) and superficial Rockwell hardness values (0-78 HR15Y). Abradability tests have been performed using an abradable-seal test rig, capable of simulating operational wear at different rotor speeds and seal incursion rates (SIRs). These tests allowed determining the rubbing forces and quantifying the blade and seal wear characteristics for slow and fast SIRs. Erosion wear performance and ASTM C633 coating adhesion strength test results are also reported. For optimal abradability performance, it is shown that coating hardness needs to be lower than 70 and 50 HR15Y for slow and fast blade incursion rate conditions, respectively. It is shown that the erosion wear performance, as well as, the coating cohesive strength is a function of the coating hardness. The current results allow defining the coating specifications in terms of hardness and porosity for targeted applications.

Experimental Evaluation of Abradable Seal Performance at High Temperature

Abradable seals have been used in aero-engines and land-based gas turbines for more than three decades. They are applied to various sections of the engine in order to reduce gas leakage by optimizing the gap between rotating and stationary parts. This optimization represents a significant increase in efficiency and decrease in fuel consumption. Performance evaluation of any abradable seal includes measurement of its mechanical properties, abradability tests and (ultimately) tests in engines. The aim of this paper is to study the effect of temperature on the rub performance of abradable seals. A series of experiments has been carried out in order to evaluate a commercially available seal material at different operating conditions. The effect of operating temperature on contact force, abrasion scar appearance and blade wear is examined and analyzed. A microstructural analysis of the rub scar has also been performed.Copyright

Sensitivity of air-coupled ultrasound and eddy current sensors to bearing fault detection

For decades, vibration and oil analysis have usually been used to detect early bearing faults and track their progression over time. Progress has been seen in condition monitoring through vibration analysis of rolling element bearings using improved sensors and advanced signal processing techniques. In this paper, the authors investigate the use of air-coupled ultrasound and eddy current sensors as diagnostic tools for the detection of bearing faults. A series of experiments was carried out in a laboratory environment: localized defects with different sizes were created intentionally on the test bearing components simulating evolving cracks or other related faults. The resulting data for a constant bearing speed and load have shown that both sensors are capable of detecting different types of defects located on the bearing components. The data from the air-coupled ultrasound and eddy current sensors were also compared with those obtained from an accelerometer. The test method and the processing technique are described and the spectra of the different signals are analyzed and discussed.

Experimental Evaluation of Foil Bearing Performance: Steady-State and Dynamic Results

An experimental facility dedicated to measuring both the steady-state and dynamic properties of foil bearings, under a variety of operating conditions, has been designed and commissioned. The bearing under test is placed at the midspan of a horizontal, simply-supported, stepped shaft which rotates at up to 60 krpm. Static and dynamic loads of up to 3500 N and 450 N (respectively) can be applied by means of a pneumatic cylinder and two electrodynamic shakers. This paper outlines the test procedures and data analysis methods pertaining to the operation of the high-speed, oil-free bearing test rig, and presents steady-state and dynamic results for a first-generation foil bearing. The test bearing, which was fabricated in-house, is 0.07 m diameter and has an aspect ratio of 1; bearing manufacturing details are provided.© 2009 ASME

Effect of Surface Texturing on the Steady-State Properties and Dynamic Coefficients of a Plain Journal Bearing: Experimental Study

The last decade has seen a significant and increased interest in surface texturing technologies esulting in improving the overall tribological properties of mechanical components. Several techniques could be used to modify the surface topography with laser surface texturing becoming most popular recently. In this investigation, rig experiments have been performed on plain and textured-surface journal bearings with an aspect ratio of 1.1 under a variety of loads and speeds. Percussive burnishing (embossing) was used to create the dimples on the internal surfaces of the test bearings. The dimples have a spherical shape with a diameter of 1 mm and a depth of 60 micrometers. Pit-area ratio was in the range 5–20% of the total bearings surfaces. The effects of surface-texturing and dimple density on the bearing steady-state characteristics and dynamic coefficients are analyzed and discussed in this paper.Copyright

A Comparative Study of Air-Coupled Ultrasound Sensor and Accelerometer in Detecting Bearing Defects

The aim of this preliminary study is to investigate the capabilities of a non-destructive evaluation (NDE) sensor in detecting bearing faults. An air-coupled ultrasound sensor is used for this purpose. An accelerometer, which is the standard sensor used in industry, is also used in order to compare the output spectrums of the two sensor signals. A defect was created intentionally on the bearing components to simulate a fatigue crack or other relevant defect. The power spectra of vibration signals measured by accelerometer and ultrasound sensor are compared and their advantages and disadvantages are determined.© 2005 ASME

A Comparison of the Steady-State and Dynamic Performance of First- and Second-Generation Foil Bearings

Oil-free foil bearing technology has advanced intermittently over the years, driven by research efforts to improve both steady-state and dynamic performance characteristics, namely: load capacity, stiffness, and damping. Bearing designs are thus classified according to “generation”, with first-generation bearings being the most primitive. This paper presents an experimental evaluation of a first- and a second-generation foil bearing, and aims to provide the high-fidelity data necessary for proper validation of theoretical predictive models of foil bearing performance. The aforementioned test bearings were fabricated in-house, and are both 70mm in diameter with an aspect ratio of 1; bearing manufacturing details are provided. The work makes use of a facility dedicated to measuring both the steady-state and dynamic properties of foil bearings under a variety of controlled operating conditions. The bearing under test is placed at the midspan of a horizontal, simply-supported, stepped shaft which rotates at up to 60krpm. Static and dynamic loads of up to 3500N and 450N (respectively) can be applied by means of a pneumatic cylinder and two electrodynamic shakers. The bearings’ structural (static) stiffnesses are highly nonlinear, and this affects the accuracy of the dynamic coefficient determination. Both dynamic stiffness and damping are found to vary nonlinearly with excitation frequency, and are over-predicted by a structural experimental evaluation — the film plays an important role in bearing dynamics. The second-generation bearing is found to have a higher load capacity, dynamic stiffness, and damping than the first-generation bearing.Copyright