\n This paper offers an extensive review of publications dealing with the modeling, the design, and the experimental investigation of grooved dynamic gas-lubricated bearings. Recent years have witnessed a rise in small-scale and high-speed turbomachinery applications. Besides the well-known gas foil bearings, grooved bearings offer attractive advantages, which unveil their potential in particular at small scale due to the structural simplicity as well as satisfying predictability. This paper starts with a general background of the application of gas-lubricated bearings and introduces and compares the different gas bearing topologies. Further, the state-of-the-art modeling of grooved gas-lubricated bearings is introduced, systematically assessing the advantages and inconveniences of two major approaches, i.e., the narrow groove theory (NGT) and direct discretization method. Since the NGT method is an elegant and efficient approach to model the complex effects of periodic grooves, a critical section is dedicated to the NGT. In a second phase, different models to include additional physical phenomena such as real gas lubrication, rarefaction, or turbulence effects are reviewed. The paper concludes with a critical assessment of the state-of-the-art and indicates potential fields of research that would allow to shed more light into the understanding of these bearings, as well as with some thoughts on the integrated design methodologies of gas bearing supported rotors.

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A Review of Grooved Dynamic Gas Bearings

A transient hydrodynamic lubrication comparative analysis for misaligned micro-grooved bearing considering axial reciprocating movement of shaft

Recently, herringbone-grooved journal bearings have had important applications in miniature rotating machines. The scribed grooves, on either the rotating or stationary member of the bearing, can pump the lubricant inward, which generates supporting stiffness and improves the dynamic stability, especially for concentric operation. Most of the previous investigations that dealt with herringbone grooved journal bearings and grooved thrust bearings were theoretical. Few experimental attempts for the investigation of the performance characteristics of herringbone grooved journal bearings (HGJBs) and grooved thrust bearings have been done. All these investigations concentrated on rectangular and circular groove profiles of HGJBs. In order to improve the performance characteristics of HGJBs, a new design of the groove profile, the beveled-step groove profile, is introduced. The introduced groove profile is capable of increasing the pressure recovery at the divergence of the flow over the step. In addition, it increases the amount of oil pumped inward over the circular groove profile. Optimization processes were carried out experimentally, in order to obtain the optimal geometry of the introduced groove profile. The optimum geometrical parameters of the groove (groove angle a, groove width ratio β, and groove depth ratio T) are 29 deg, 0.5, and 2.0, respectively, which give maximum radial force and maximum radial stiffness of the beveled-step HGJB. In order to check the effectiveness of the introduced beveled-step groove profile, the obtained results were compared with that for rectangular groove profile. The comparison shows that the introduced beveled-step HGJBs have higher radial force, higher load carrying capacity, and lower friction torque than the rectangular HGJBs.

On the Optimum Groove Geometry for Herringbone Grooved Journal Bearings

Effect of support stiffness and damping on stability characteristics of herringbone-grooved aerodynamic journal bearings mounted on viscoelastic supports

Rotors supported by active magnetic bearings (AMBs) can spin at high surface speeds with relatively low power losses. This makes them particularly attractive for use in flywheels for energy storage in applications such as electric vehicles and uninterruptible power supplies. In order to optimize efficiency in these and other applications, the loss mechanisms associated with magnetic bearings and rotating machinery must be well understood. The primary parasitic loss mechanisms in an AMB include complex magnetic losses, due to eddy currents and hysteresis, and windage losses along the entire rotor in nonvacuum environments. In low-loss magnetic bearing designs, the windage loss component along the rotor can become dominant at high speeds, and the need for accurate windage models becomes even more critical. This study extends previous AMB power loss work by evaluating five different windage loss models using the experimental rundown data from the previous work. Each of the five windage models, along with standard models of eddy current and hysteresis losses, are used to reduce the rundown data into the associated power loss components. A comparison is then completed comparing the windage power loss component extracted through the rundown data reduction scheme to the associated analytical windage prediction in order to identify the most accurate model for calculating windage losses along a smooth rotor. Five empirical flat-plate drag coefficient models are implemented, four turbulent and one laminar. An empirical flat-plate turbulent boundary layer formula (referred to here as "Model 2") developed by Prandtl and Schlichting displayed the best agreement between experimentally extracted and analytically predicted windage loss values. The most accurate model formula (Model 2) dictates that the frequency dependency of windage loss is both logarithmic and power based and represents the minimum error between experimentally extracted and analytically predicted losses of all models in the study of high-speed power losses in a smooth rotor supported in AMBs.

Windage Power Loss Modeling of a Smooth Rotor Supported by Homopolar Active Magnetic Bearings

A laser scanner motor with low power and high speed has been developed. This scanner motor uses a herringbone-grooved journal bearing which functions as a viscous vacuum pump. The windage power loss of a polygon mirror is reduced, since the air inside the pump housing is pumped out by herringbone-grooved viscous vacuum action. In this paper, the theoretical pumping characteristic of this bearing is investigated, using the narrow-groove theory and accounting for first-order slip flow. The effects of various design parameters on the pumping characteristics are discussed. Optimum geometric design parameters were found to obtain the minimum inner chamber pressure of the housing. The theoretical predictions considering slip flow effects are in good agreement with experimental measurements.

Pumping Characteristics of a Herringbone-Grooved Journal Bearing Functioning as a Viscous Vacuum Pump

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Pumping Characteristics of a Herringbone-Grooved Journal Bearing Functioning as a Viscous Vacuum Pump