Hybrid Gas Bearings Research Articles

A Thermal Model for a Hybrid Gas Bearing System in Oil-Free Turbochargers

Abstract With little drag friction, gas bearings operate at high rotor speed and high temperature and thus enable long operating life along with material damping for mechanical energy dissipation. However, most computational tools for modeling gas bearings are not accessible to bearing manufacturers or potential end-users, and the models are restricted to specific geometries and operating conditions or are missing important features, thus limiting their utility. This paper presents the thermal energy transport in a hybrid gas bearing (HGB) for oil-free turbochargers (TCs) with integrated heat and fluid flow models to produce a comprehensive thermohydrodynamic analysis predictive tool and to design and evaluate air-lubricated gas bearings by predictions and experiments. An efficient algorithm couples the solution of the Reynolds equations and the thermal energy transport equations in the film between the rotor and a pad of the hybrid gas bearing and updates the temperature-dependent viscosity and film thicknesses during the iterative process. The balance of the bulk-flow thermal energy transport is that the summation of drag power losses plus heat convection into the film equals to the thermal energy advected by the film. The predictions show that the film temperature varies along circumferential and axial directions by following the balance of the energy flows and shows high film temperatures corresponding to the small film thicknesses and thus large film pressures. The predicted result also shows that the peak temperature of the film occurs at the exit side of the film near the trailing edge of each pad. Thermocouples installed axially at the leading and trailing edges of each pad measure temperature of the film to validate the thermal module. The test repeats and averaged for each rotor speed from 2 krpm to 22 krpm at intervals of 2 krpm, for supply pressure varying along 25 psi to 100 psi, and predicted film temperature matches well with the measured one. The parameters of interest in this analysis include the gas supply condition, bearing configuration, and the gas properties at high altitudes and high rotation speeds. The parametric study results show that the density and kinematic viscosity are the most dominant properties of the gas lubrication for the film temperature.

On the Pneumatic Hammer of Hybrid Gas Bearings: Measurements and Predictions

Abstract Hybrid bearings integrating an external pressurizing source are widely used in high-speed turbomachinery due to their notable advantages, including low friction and wear, enhanced reliability and durability, and accurate rotor positioning, as well as large static stiffness and load carry capacity even lubricated with low viscosity liquids. This paper reports experimental data and predictions to identify the characteristics of pneumatic hammer of hybrid gas bearings, 60 mm in diameter, with increasing feed gas pressures. Pneumatic hammer characteristics with static load stiffnesses and flow rates of the test bearing are recorded for increasing static loads with various shaft center positions. A computational program for modeling of hybrid gas bearings predicts static load characteristics of the test bearings. Predictions show a remarkable agreement with measurements. Comparisons of measurements and predictions reveal that calculated reduced damping factors and damping coefficients of hybrid bearings, relying on volume ratio between recess and fluid film, are reliable indicators to estimate the onset condition of pneumatic hammer instability.

Numerical and Experimental Investigation on Axial Rub Impact Dynamic Characteristics of Flexible Rotor Supported by Hybrid Gas Bearings

Gas bearings are widely used in micro- and small turbomachinery. Because of the pursuit of high efficiency, turbomachinery adopts small clearance of rotor and stator. The gas bearing rotor system easily suffers from rub impact due to the inherently low damping and load capacity of gas film. Axial rub impact may lead to catastrophic failure of gas bearing rotor system. Previous work put emphasis on radial rub, and only a few papers researched on the axial rub impact by simulation method. In this paper, dynamic responses of full annular axial rub are investigated numerically and experimentally. A single span flexible rotor test rig is established to support this research. Dynamic characteristics of full annular axial rub of this gas bearing rotor system are obtained with finite element language-APDL. Dynamic characteristics within full speed range are experimentally researched based on the test rig. The dynamic behaviors are analyzed by means of waterfall diagrams, frequency spectrums, orbit trails, and vibration amplitude waveforms. During speed up, half speed whirl and gas film oscillation occur in radial direction. During speed down, the full annular axial rub between rotor thrust disk and gas bearing occurs. When lightly axial rub impact happens, the vibration patterns in the radial direction change barely, and 0 Hz component appears in the axial direction. When serious full annular axial rub impact happens, 0 Hz component occurs in both radial and axial directions and rotor orbit shows transverse motion in radial direction. These forms of dynamic characteristics can be effectively used to diagnose the full annular axial rub impact.

Experiments With a Rotor-Hybrid Gas Bearing System Undergoing Maneuver Loads From Its Base Support

Abstract Gas bearings enable microturbomachinery (MTM) with a large power to weight ratio, low part count, and nearly frictionless motion, thus resulting in systems operating over extended maintenance intervals and with improved fuel efficiency. Envisioned oil-free vehicle transportation systems implementing gas bearings range from small size gas turbines, to unmanned aerial vehicles, to turbochargers (TC), and more to come. In these vehicles, base or support transient displacements transmit forces exciting the rotor-bearing system; hence, the need to characterize system integrity under stringent operating conditions. This paper reports experiments demonstrating the ability of a hybrid gas bearing-rotor system to withstand maneuver actions that suddenly remove the ground support. The test rig consists of a rigid motor-rotor, supported on tilting pad hybrid gas bearings supplied with pressurized air. The rotor is housed in a thick steel casing that is attached to a rigid base plate. The whole test rig hangs from a crane; two steel cables connect to one side of the base and a nylon webbing attaches to the other side of the base. The other end of the webbing ties to a release mechanism, which when released, frees one side of the rig base. Suddenly, the whole test rig rotates and displaces downward while the tensions in the taut cables rapidly increase and pull the test rig as it swings back and forth. The crane support enables two release maneuvers: one turns the rig ∼90 deg and the other flips it 180 deg, both events occurring while the rotor spins at 70 krpm (surface speed 105 m/s). The measured rotor displacements relative to the casing demonstrate a momentary increase in motion amplitude, up to ∼1.15 mm since the bearings also displace, along with a maximum casing deceleration of ∼7 g when the cables stop the rig fall. The measurements show the rotor response is free of subsynchronous whirl frequencies that could evidence a rotor dynamic instability. Very low frequency motions denote the swing frequency of the hanging rig and jerk motions from the crane lifting and bouncing when the rig is at its lowest vertical position. In one instance, power to the motor unexpectedly interrupted and the rotor underwent an unplanned shaft speed coastdown. In spite of the large displacements recorded, the rotor survived both events; it continues to operate to this day. The experiments demonstrate that the hybrid gas bearing system could withstand large amplitude rotor excursions. The measurements provide a novel method for testing gas bearings, as the induced excitations are multidirectional, while the test rig encounters a short period of free falling, followed by a quick deceleration with large forces. A simple kinetics model of the test rig drop produces peak decelerations similar in magnitude to those measured.

Research on dynamic characteristics of gas film of spherical hybrid gas bearings based on computational fluid dynamics

A realizable k–ε turbulence model for spherical spiral groove hybrid gas bearing films was established based on computational fluid dynamics (CFD). A six degrees of freedom passive grid was used to calculate the gas film pressure distribution, bearing capacity, and dynamic characteristic coefficients numerically. The gas flow field dynamic and static pressure coupling mechanism was studied. The effects of the rotation speed, gas film thickness eccentricity ratio, and gas supply pressure on the dynamic and static pressure bearing capacity, and dynamic characteristic coefficients during operation were analyzed as a method of research into the mechanical mechanisms of gas bearing stability. The CFD calculation analysis can simulate the complex gas flow in the transient flow field of the gas film and determine reasonable operation parameters to optimize the dynamic and static pressure coupling effects, which can improve the gas film bearing capacity, dynamic characteristics, and operational stability of gas bearings.

Experimental Rotordynamic Force Coefficients for a Diffusion Bonded Compliant Hybrid Journal Gas Bearing Utilizing Fluid-Filled Hermetic Dampers

Abstract Dynamic force coefficients are presented from experimental results of a radial gas bearing with hermetically sealed squeeze film dampers (HSFDs) in the bearing support. HSFDs are a relatively new technology aimed to increase damping levels in gas bearings while sustaining an oil-free bearing sump. Past HSFD designs proved bulky and contained many components making it difficult to employ in size-limited environments such as jet engines, while the diffusion bonded bearing discussed in this paper provides a compact integral design. Details of the design are found in a companion paper by Ertas (Ertas, B. H., 2019, “Compliant Hybrid Gas Bearing Using Integral Hermetically-Sealed Squeeze Film Dampers,” ASME Paper No. GT2018-76312). Test results for a 3 in. (76.2 mm) diameter bearing using a test rig providing static loads up to 80 lbs (356 N), controlled-dynamic orbital motion, and speeds up to 27 krpm are shown. Results include frequency- and speed-dependent direct and cross-coupled rotordynamic force coefficients. Dynamic testing showed little dependence on rotor speed or static load and exhibited frequency dependency at lower excitation frequencies. Cross-coupled terms are generally an order of magnitude lower than direct terms. Results show the direct stiffness coefficients increasing with frequency, while direct damping decays radically with frequency. Comparison of the overall gas bearing coefficients with the companion paper (Ertas, B. H., 2019, “Compliant Hybrid Gas Bearing Using Integral Hermetically-Sealed Squeeze Film Dampers,” ASME Paper No. GT2018-76312), showing bearing support coefficients, reveals a drastic reduction in damping when engaging the gas film. The results also indicate that the bearing can withstand vibration levels representative of a large rotor system critical speed at lower excitation frequencies.

Optimum Compression in a Wave Compressor with Hybrid Gas Bearings

The concept of a wave compressor using a centered isentropic wave for air compression is considered, and shock-wave structures are studied, which are arisen when a centered wave is focused. It is concluded that the characteristic centered compression wave with reflected weak discontinuity is optimal.

Study on dynamic characteristics of gas films of spherical spiral groove hybrid gas bearings

According to the gas film force variation law, when the bearing axis is slightly displaced from the static equilibrium position, displacement and velocity disturbance relation expressions for the gas film force increment are constructed. Moreover, combined with the bearing rotor system motion equation, calculation model equations for the gas film stiffness and damping coefficients are established. The axial and radial vibration and velocity of the gas bearings during operation are collected. The instantaneous stiffness and damping coefficients of the gas film are calculated by the rolling iteration algorithm using MATLAB. The dynamic changes in the gas film stiffness and damping under different motion states are analyzed, and the mechanism of the gas film vortex and oscillation is studied. The results demonstrate the following: (1) When the gas bearing is running in the linear steady state in cycle 1, the dynamic pressure effect is enhanced and the stability is improved by increasing the eccentricity; when the gas supply pressure is increased, the static pressure effect is enhanced and the gas film vortex is reduced, but the oscillation is strengthened. (2) With the increase in rotational speed, the gas film vortex force gradually exceeds the gas film damping force, and the stability gradually worsens, causing a fluctuation in the gas film stiffness and damping, following which singularity occurs and a half-speed vortex is formed. Meanwhile, the gas film oscillation is intensified, and the rotor enters the nonlinear stable cycle 2 state operation. (3) As the fluctuation of the film force increases, the instantaneous stiffness and damping oscillation of the film intensifies, most of the stiffness and damping coefficients exhibit distortion, and the rotor operation will enter a chaotic or unstable state. Therefore, the gas bearing stiffness and damping variation characteristics can be used to study and predict the gas bearing operating state. Finally, measures for reducing the vortex and oscillation of the gas film and improving the stability of the gas bearing operation are proposed.

Flow field calculation and dynamic characteristic analysis of spherical hybrid gas bearings based on passive grid

In order to research the spherical spiral groove hybrid gas bearings, the Realizable k − e turbulence model of gas film was established based on FLUENT. The simulation calculation method of 6-degrees of freedom passive grid was used, which can simulate the lubrication characteristics of the gas film transient flow field accurately. And the gas film pressure distribution and dynamic characteristic coefficients are numerically calculated. The dynamic and static pressure coupling effects of the gas flow field were analyzed, and the axis motion trajectory was simulated. The effect of rotation speed, gas supply pressure and tangential angle on the dynamic characteristic coefficients during bearing operation was analyzed. And the stability of the gas bearing was studied. The conclusion from the analysis shows that different rotation speed and gas supply pressure will change the pressure distribution of the gas bearing during the operation. The dynamic characteristics of the gas film can be changed by reasonably optimizing the operation parameters, which can change the whirl characteristics of the gas film and improve the stability. Through calculation and analysis, the tangential angle is selected between 55° and 60°, to ensure that the gas film has a high stiffness, while it also can obtain the larger damping. The simulation results and the experimental results are compared and analyzed to verify the correctness and effectiveness of the simulation method. At the same time, the research of this paper provided a theoretical basis for optimizing the bearing structure and operating parameters, improving the dynamic characteristics of gas bearings and improving the operation stability.

Dynamic Characterization of a Novel Externally Pressurized Compliantly Damped Gas-Lubricated Bearing With Hermetically Sealed Squeeze Film Damper Modules

Ever-increasing demand for cleaner energy is driving the need for higher power density turbomachinery while reducing cost and simplifying design. Gas-lubricated bearings are representing one of the enabling technologies that can help maximize these benefits and have been successfully implemented into turbomachinery applications with rotors weights in the order few kg's. However, load capacity and damping limitations of existing gas bearing technologies prevent the development of larger size oil-free drive trains in the MW power output range. Compliantly damped hybrid gas bearings (CHGBs) were introduced as an alternative design to overcome these limitations by providing external pressurization to discrete tilting pads while retaining flexibility in the bearing support to help tolerate misalignment and rotor-pad geometry changes. Additionally, the CHGB concept addresses damping entitlement through the application of bearing support dampers such as metal mesh. An alternative CHGB design, featuring a novel hermetically seal squeeze film damper (HSFD) in the bearing support, was introduced as alternative approach to metal mesh dampers (MMDs) to further improve bearing damping. This paper details the rotordynamic characterization of a CHGB with modular HSFD for various operating conditions. Direct and cross-coupled stiffness and damping coefficients are presented for different rotor speeds up to 12,500 rpm, frequencies of excitation between 20 and 200 Hz, bearing loads between 200 and 400 lbf, and external hydrostatic pressures reaching 180 psi. Direct comparisons to experimental results for a CHGB using MMD show 3× increase in direct damping levels when using HSFD in the compliant bearing support. In addition to the experimental results, an analytical model is presented based on the implementation of the isothermal compressible Reynolds equation coupled to a flexible support possessing a pad with three degrees-of-freedom. The numerical results capture the direct stiffness and frequency dependency but underpredict the absolute values for both cases when compared to experimental data.

Compliant Hybrid Gas Bearing Using Modular Hermetically Sealed Squeeze Film Dampers

This paper presents a new gas bearing concept that targets machine applications in the megawatt (MW) power range. The concept involves combining a compliant hybrid gas bearing (CHGB) with two hermetically sealed squeeze film damper (HSFD) modules installed in the bearing support damper cavities. The main aim of the research was to demonstrate gas bearing-support damping levels using HSFD that rival conventional open-flow squeeze film dampers (SFD) in industry. A detailed description of the bearing design and functionality is discussed while anchoring the concept through a brief recap of past gas bearing concepts. Proof-of-concept experimental testing is presented involving parameter identification of the bearing support force coefficients along with a demonstration of speed and load capability using recessed hydrostatic pads. Finally, a landing test was performed on the bearing at high speed and load with porous carbon pads to show capability of sustaining rubs at high speeds. The component testing revealed robust viscous damping in the bearing support, which was shown to be comparable to existing state of the art SFD concepts. The damping and stiffness of the system-portrayed moderate frequency dependency, which was simulated using a 2D Reynolds-based incompressible fluid flow model. Finally, rotating tests demonstrated the ability of the gas bearing concept to sustain journal excursions and loads indicative of critical speed transitions experienced in large turbomachinery.

Dynamic Force Coefficients of Hydrostatic Gas Films for Recessed Flat Plates: Experimental Identification and Numerical Predictions

The following paper focuses on an experimental and analytical study aimed at identifying the dynamic force coefficients of hydrostatic gas films for recessed flat plates. The motivation for the effort was brought upon by the necessity of generating more accurate models for hydrostatic gas films found in hybrid gas bearings. Pressurized air at room temperature up to 120 psi was used to test different recess geometries on a flat plate test rig, capable of characterizing the stiffness and damping force coefficients for varying supply pressures, gas film thickness values, excitation frequencies, and vibration amplitudes. The test rig design and operation is described. Experimental results include frequency-dependent stiffness and damping coefficients, and leakage. The test results show that using external pressurization can generate large stiffness values while exhibiting small leakage. However, the results also show that the majority of the test configurations portray high negative damping values. An analytical model is presented and numerical predictions are compared to experimental results. Example damping trends as a function of frequency, pressure, and film thickness are presented in addition to force coefficient plots as functions of pressure ratio.

Analysis of dynamic characteristics and stability prediction of gas bearings

PurposeThe prediction model to estimate the stability of a rotor-bearing system is established, which can predict the stability of gas bearings by applying Routh–Hurwitz stability criterion. This paper aims to provide the theoretical foundation for controlling actively the bearing running stiffness and damping and stemming the instability of a gas film.Design/methodology/approachThe nonlinear dynamic lubrication analysis mathematical model of spherical hybrid gas bearings is established. Perturbation control equation is derived by the partial derivative method. The finite difference method is used to discrete the perturbation control equation in generalized coordinate system, and the difference expression of perturbation pressure is derived. The relational expression which involves the relationship between the dynamic characteristic coefficients of HSGHGB systems and perturbation pressure is deduced. So, the transient perturbation pressure distribution of a three-dimensional micro gas film, nonlinear gas film force, dynamic stiffness and dynamic damping coefficients of bearings are numerically computed using VC++6.0 programs.FindingsThe results show that the influence of supply pressure, speed and eccentricity on the dynamic characteristics of bearings is significant.Originality/valueThe influence law of supply pressure, speed and eccentricity ratio on the dynamic stiffness and damping coefficients of HSGHGB systems is researched. The prediction model to estimate the stability of rotor-bearing system is established, which can predict the stability of gas bearings by applying the Routh–Hurwitz stability criterion.

Dynamic Stability Prediction of Spherical Spiral Groove Hybrid Gas Bearings Rotor System

Taking the hemisphere spiral groove hybrid gas bearings (HSGHGB) as the research object, the nonlinear dynamic lubrication analysis mathematical model of spherical hybrid gas bearings is established with the axis instantaneous position and instantaneous displacement speed as the parameters. The perturbation pressure control equation is solved by means of the finite difference method in generalized coordinate system. The calculation program is prepared based on VC++6.0, and the transient perturbation pressure distribution of three-dimensional (3D) gas film, nonlinear gas film force, and dynamic stiffness and damping coefficients are numerically calculated. The influences of different speeds, eccentricity ratios, and gas supply pressures on the dynamic characteristic coefficients of gas film are studied. The results show that the influence of bearing's supply pressure, speed, and eccentricity on the dynamic characteristics of gas film is significant. The dynamic equations of rotor-bearing system containing the gas film dynamic stiffness and the damping coefficients are established, and the stability of the gas film is predicted based on the Routh–Hurwitz stability criterion. The research provides the theoretical foundation for actively controlling the bearing running stiffness and damping and stemming the instability of gas film.

Adjustable hybrid gas bearing – Influence of piezoelectrically adjusted injection on damping factors and natural frequencies of a flexible rotor operating under critical speeds

Damping factors and natural frequencies of a flexible rotor supported by a gas bearing with piezoelectrically adjusted flow, are theoretically determined using a rotor finite element model coupled with the modified Reynolds equation. An extra term is added to the standard formulation of Reynolds equation aiming at incorporating the effect of the adjustable external pressurized inlet flow. Two different configurations are theoretically as well as experimentally studied: (a) the air is injected from a single orifice positioned at the bottom of the bearing and (b) the air is injected through four radial injectors equally pressurized. For the two configurations, the theoretical results are experimentally validated as a function of the piezoactuators input voltage and the journal angular velocity. Results show a good agreement for natural frequencies and damping factors. Theoretical and experimental results show qualitatively as well as quantitatively that the injectors position and the injection flow (dependent on the piezoactuator input voltage) have an important influence on the dynamic characteristics of the rotor-bearing system. By using one single injector positioned at the bearing bottom, the damping factor associated with the first mode shape can be increased by 10 times when compared to four injectors equally pressurized.

Steady state characteristics of an adjustable hybrid gas bearing – Computational fluid dynamics, modified Reynolds equation and experimental validation

To include the effect of external pressurization in hybrid gas bearings an extra term is added to Reynolds Equation to accommodate the gas jet. Two cases are considered: cylindrical and annular flow profiles. Validation of theoretical results obtained using the modified version of Reynolds equation for compressible fluid against computational fluid dynamics (CFD) model is presented in terms of pressure and flow rate considering pressurization levels, journal eccentricities and angular velocities. Correction factors for the jet discharge coefficients are necessary and calculated added by CFD model. By introducing such coefficients into the modified Reynolds equation, good agreement with experiments is achieved in terms of journal equilibrium position and resulting aerodynamic forces.

Experimental Identification of Dynamic Force Coefficients for a 110 MM Compliantly Damped Hybrid Gas Bearing

Compliant hybrid gas bearings (HGBs) combine key enabling features from both fixed geometry externally pressurized gas bearings and compliant foil bearings. The compliant hybrid bearing relies on both hydrostatic and hydrodynamic film pressures to generate load capacity and stiffness to the rotor system, while providing damping through integrally mounted metal mesh bearing support dampers. This paper presents experimentally identified force coefficients for a 110 mm compliantly damped gas bearing using a controlled-motion test rig. Test parameters include hydrostatic inlet pressure, excitation frequency, and rotor speed. The experiments were structured to evaluate the feasibility of implementing these bearings in large size turbomachinery. Dynamic test results indicate weak dependency of equivalent direct stiffness coefficients to most test parameters except for frequency and speed, where higher speeds and excitation frequency decreased equivalent bearing stiffness values. The bearing system equivalent direct damping was negatively impacted by increased inlet pressure and excitation frequency, while the cross-coupled force coefficients showed values an order of magnitude lower than the direct coefficients. The experiments also include orbital excitations to simulate unbalance response representative of a target machine while synchronously traversing a critical speed. The results indicate the gas bearing can accommodate vibration levels larger than the set bore clearance while maintaining satisfactory damping levels.

Nonlinear dynamic characteristics of rotating ramjet rotor supported by hybrid gas bearing

The nonlinear dynamic characteristics of rotating ramjet rotor supported by hybrid gas bearing are studied. The compression inlet flow field at different back pressure levels is analyzed and the normal working back pressure level is determined. The periodic movement phenomenon of normal shock wave in compression inlet is presented. The influence on the compression inlet flow field with the variation of structure dimension is introduced. Then, the nonlinear compression inlet flow force generated from the whirling of the rotor is obtained. The model for the rotating ramjet rotor supported by the hybrid gas bearing is established by the finite element method. The equation of motion for the rotating ramjet rotor is numerically solved and coupled with the gas lubricated Reynolds equation considering the time terms. The vibration characteristics of the rotating ramjet with different supply pressure and unbalanced mass eccentricities are solved by the Newmark method. The orbit trajectory diagram, frequency spectrum diagram, and time response diagram are obtained. Then, the stability of the rotating ramjet rotor system is discussed. The results indicate that the compression inlet is under the condition of high adverse pressure gradient, the shock wave, expansion wave, reflections and crossings of the shock waves, boundary layer–shock wave interference, and separation of the flow, which lead to the unstable flow of the compression inlet. The nonlinear compression inlet flow force can cause sub-synchronous vibration. If the supply pressure and eccentricities are properly designed, the vibration amplitudes can be decreased and the stability will be improved, which will make the foundation for the vibration control of the rotating ramjet system.

Application of a forecasting coupling method to the non-linear dynamic analysis of a flexible rotor supported by externally pressurized orifices hybrid gas bearings

The non-linear dynamic characteristics of a flexible rotor supported by externally pressurized hybrid gas bearings are studied in this article. The rotor dynamic equations for the rotor are solved by the Newmark integral method and the gas-lubricated Reynolds equation by the alternating direction implicit method. The multifield coupling algorithm based on the forecasting method is proposed and applied in this article to solve the fluid–structure interaction problem. Also, the non-linear dynamic parameter identification method based on the forecasting orbit method is investigated. It is indicated that the dynamic characteristics of externally pressurized hybrid gas-bearing rotor system and whirling instability of the system reveal the complex behaviour, which could be depicted comprehensively. This would establish the foundation for contributing to a further understanding of the hybrid gas-bearing flexible rotor system.

Hybrid Gas Bearings With Controlled Supply Pressure to Eliminate Rotor Vibrations While Crossing System Critical Speeds

Microturbomachinery implements gas bearings in compact units of enhanced mechanical reliability. Gas bearings, however, have little damping and wear quickly during transient rub events. Flexure pivot tilting pad bearings offer little or no cross-coupled stiffnesses with enhanced rotordynamic stability; and when modified for hydrostatic pressurization, demonstrate superior rotordynamic performance over other bearing types. External pressurization stiffens gas bearings thus increasing system critical speeds, albeit reducing system damping. Most importantly, measurements demonstrate that external pressurization is not needed for rotor supercritical speed operation. In practice, the supply pressure could be shut off at high rotor speeds with substantial gains in efficiency. This paper introduces a simple strategy, employing an inexpensive air pressure regulator to control the supply pressure into the hybrid bearings, to reduce or even eliminate high amplitudes of rotor motion while crossing the system critical speeds. Rotor speed coast-down tests with the pressure controller demonstrate the effectiveness of the proposed approach. A simple on-off supply pressure control, i.e., a sudden increase in pressure while approaching a critical speed, is the best since it changes abruptly the bearing stiffness coefficients and moves the system critical speed to a higher speed. A rotordynamic analysis integrating predicted bearing force coefficients forwards critical speeds in agreement with the test results. Predicted rotor responses for the controlled supply conditions show an excellent correlation with measured data. The experiments validate the predictive tools and demonstrate the controllable rotordynamic characteristics of flexure pivot hybrid gas bearings.