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Jürg Alexander Schiffmann - One of the best experts on this subject based on the ideXlab platform.
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An Instrumented High-Speed Rotor With Embedded Telemetry for the Continuous Spatial Pressure Profile Measurement in Gas Lubricated Bearings: A Proof of Concept
Journal of Engineering for Gas Turbines and Power, 2020Co-Authors: K. Shalash, Jürg Alexander SchiffmannAbstract:Abstract Pressure is the constitutive quantity governing the flow field in Gas Lubricated Bearings. Knowledge of the pressure is of principal importance in the fundamental understanding of such Bearings as well as for the validation of their models. Pressure measurements can be done from the bearing side using pressure taps, yet, several details will not be captured. In order to acquire a continuous scan of the pressure field inside the bearing, it is necessary to measure from the rotor side. This paper presents an instrumented measurement high-speed rotor with embedded pressure probes and a wireless telemetry that is capable of the continuous pressure field measurement within the Gas film of journal Bearings. The rotor was tested on externally pressurized Gas journal Bearings (EPGJBs) (D = 40 mm and L/D = 1), and pressure profile measurements were acquired up to 37.5 krpm (DN 1.5 M). Measurements at discrete points using pressure taps inside the test bearing were also performed for comparison. The measurements from both sides (bearing and rotor) were in good agreement at quasi-static conditions. At higher operational speeds, it was necessary to perform an in situ system identification and calibration for the embedded pressure probes using the bearing side measurements as a reference. The in situ system identification technique was successful to reconstruct the attenuated pressure signals for a wide range of supply pressures (amplitudes) and rotor speeds (excitation frequencies). The instrumented rotor was proven qualified to perform time-resolved pressure measurements within the Gas film of journal Bearings up to 37.5 krpm.
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A Review of Grooved Dynamic Gas Bearings
Applied Mechanics Reviews, 2019Co-Authors: Eliott Guenat, Jürg Alexander SchiffmannAbstract:Abstract 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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An Instrumented High-Speed Rotor With Embedded Telemetry for the Continuous Spatial Pressure Profile Measurement in Gas Lubricated Bearings: A Proof of Concept
Volume 7B: Structures and Dynamics, 2019Co-Authors: K. Shalash, Jürg Alexander SchiffmannAbstract:Abstract Gas Lubricated Bearings are capable of supporting high speed rotors with satisfactory load capacities. Pressure is one of the constitutional quantities governing the flow field in Gas Lubricated Bearings. Knowledge of the pressure is of principal importance in the fundamental understanding of such Bearings and for the calibration of reduced order models. These measurements can be done from the bearing side using pressure taps in the bushings, however, the measurement points will yield a spatially sampled profile consisting of discrete points relative to the bearing bushing. This measurement technique is simple, yet, several details cannot be captured. In order to acquire a continuous scan of the pressure field inside the bearing, it is necessary to measure from the rotor side. Such onboard measurement technique is challenging due to constraints in volume, G-force, and data and power transmission through the rotor. This paper presents an instrumented measurement rotor with embedded pressure probes and a wireless telemetry, which is capable of the continuous pressure field measurement inside a high-speed externally pressurized Gas journal bearing. The bearing under investigation has a diameter of 40mm, L/D = 1, and was tested up to 37.5 krpm. The bearing is of the annular type, with 2×18 Ø0.1mm restrictor orifices. Measurements at discrete points using pressure taps inside the test bearing were also performed for the sake of comparison. The measurements from both sides (bushing and rotor) were in good agreement at quasi-static conditions. At higher operational speeds, it was necessary to perform an in-situ system identification and calibration for the embedded pressure probes using the bearing side measurements as a reference. The in-situ system identification technique was successful to reconstruct the attenuated pressure signals for a wide range of supply pressures and rotor speeds. The instrumented rotor was proven qualified to perform time-resolved pressure measurements within the Gas film of journal Bearings up to 37.5 krpm.
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Turbocompressors for Domestic Heat Pumps – A Critical Review
2017Co-Authors: Jürg Alexander Schiffmann, Cordin Arpagaus, Jean-baptiste Carré, Stefan S. BertschAbstract:Small-scale, oil-free radial compressors on Gas Lubricated Bearings represent a promising alternative to state-of-the-art compressor technology for driving domestic sized heat pumps. The inherent characteristics of turbocompressors manage to fit the heat pump load while the oil-freeness allows the implementation of advanced heat exchanger technology and the deployment of advanced multi-stage cycles, both validated means to significantly enhance performance and efficiency. The paper presents experimental investigation and results of both electrically and thermally driven 20mm 2kW radial compressor rotating at rotor speeds of up to 210krpm. The compressor stage has been tested in R134a, reaching isentropic efficiencies above 70%. Dynamic, Gas Lubricated Bearings are supporting the high-speed rotors that are Lubricated with vapor phase working fluid, thus offering an oil-free and hermetic solution. Insights into the experimental investigation of a 6kW two-stage radial compressor for driving retrofit heat pumps with high temperature lifts are introduced as well. Besides comparing experimental data, the paper also sheds light into critical design aspects related to reduced scale machines and compares them with regards to their impact on efficiency. Identified key issues are (1) aerodynamic challenges related to the severe downscaling of radial compressors such as tip clearance, surface roughness and non-adiabatic operation (2) stable Gas bearing technology and (3) challenges related to high power density designs.
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Design of Oil-Free Turbocompressors for a Two-Stage Industrial Heat Pump under Variable Operating Conditions
2016Co-Authors: Adeel Javed, Cordin Arpagaus, Stefan S. Bertsch, Jürg Alexander SchiffmannAbstract:A pair of mechanically driven small-scale turbocompressors running on Gas Lubricated Bearings have been designed for a two-stage heat pump application functioning under variable operating conditions. Novelty in the present two-stage heat pump system lies in the application of oil-free turbocompressor technology and the introduction of unused sec-ondary heat from various sources. Managing the operational deviations and the secondary heat during off-design heat pump operation is challenging for the turbocompressors. The turbocompressors can potentially exceed their operating range defined by the surge and choke margins, and the maximum rotational speed limit set by the structural and rotor-dynamic considerations. A wide operating range is, therefore, a prerequisite design condition for the turbocompressors. The present paper will guide the readers through different stages of the design process of such turbocompressors sub-jected to various operational and design constraints. Moreover, a stochastic evaluation on the influence of variable operating conditions on the heat pump off-design performance will be detailed.
Weimin Wang - One of the best experts on this subject based on the ideXlab platform.
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Nonlinear dynamic analysis of a rotor system with fixed-tilting-pad self-acting Gas-Lubricated Bearings support
Nonlinear Dynamics, 2012Co-Authors: Yongfang Zhang, Xiaolei Shi, Weimin WangAbstract:Based on the nonlinear theory, the unbalanced responses of a fixed-tilting-pad Gas-Lubricated journal bearing-rigid rotor system are investigated. A time-dependent mathematical model is established to describe the pressure distribution of Gas-Lubricated journal bearing with nonlinearity. The rigid rotor supported by a fixed-tilting-pad self-acting Gas-Lubricated journal bearing is modeled. The differential transformation method has been employed to solve the time-dependent Gas-Lubricated Reynolds equation, and the dynamic motion equation has been solved by the direct integral method. The unbalanced responses of the rotor system supported by fixed-tilting-pad Gas-Lubricated journal Bearings are analyzed by the orbit diagram, Poincare map, time series, and spectrum diagram. The numerical results reveal periodic, period-3, and quasiperiodic motions of nonlinear behaviors of the system. Finally, the effects of pivot ratio and preload coefficient on the nonlinear dynamic characteristics of the fixed-tilting-pad self-acting Gas-Lubricated journal bearing-rotor system are investigated.
Adeel Javed - One of the best experts on this subject based on the ideXlab platform.
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Design of Oil-Free Turbocompressors for a Two-Stage Industrial Heat Pump under Variable Operating Conditions
2016Co-Authors: Adeel Javed, Cordin Arpagaus, Stefan S. Bertsch, Jürg Alexander SchiffmannAbstract:A pair of mechanically driven small-scale turbocompressors running on Gas Lubricated Bearings have been designed for a two-stage heat pump application functioning under variable operating conditions. Novelty in the present two-stage heat pump system lies in the application of oil-free turbocompressor technology and the introduction of unused sec-ondary heat from various sources. Managing the operational deviations and the secondary heat during off-design heat pump operation is challenging for the turbocompressors. The turbocompressors can potentially exceed their operating range defined by the surge and choke margins, and the maximum rotational speed limit set by the structural and rotor-dynamic considerations. A wide operating range is, therefore, a prerequisite design condition for the turbocompressors. The present paper will guide the readers through different stages of the design process of such turbocompressors sub-jected to various operational and design constraints. Moreover, a stochastic evaluation on the influence of variable operating conditions on the heat pump off-design performance will be detailed.
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Small-scale turbocompressors for wide-range operation with large tip-clearances for a two-stage heat pump concept
International Journal of Refrigeration, 2016Co-Authors: Adeel Javed, Stefan Bertsch, Cordin Arpagaus, Jürg Alexander SchiffmannAbstract:Two mechanically driven small-scale turbocompressors running on Gas Lubricated Bearings have been theoretically designed for a 6.5 kW two-stage heat pump functioning under variable operating conditions. The novelty in the heat pump system lies in the application of oil-free turbocompressor technology and the introduction of unused heat from various secondary heat sources. Managing the heat pump operational deviations with the secondary heat is difficult for the turbocompressors. The turbocompressors can potentially exceed their operating range defined by the surge, choke and maximum rotational speed margins. Furthermore, regulating the tip-leakage flow caused by large tip-clearances in small-scale turbomachinery is challenging. This paper will guide the readers through different stages of the design process of small-scale turbocompressors subjected to different operational and design constraints. The design review and the presented methodology will help the designers make suitable parameter selections for achieving high efficiency and wide compressor operating range.
G. B. Sinclair - One of the best experts on this subject based on the ideXlab platform.
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Towards a Reynolds Equation for Gas Lubricated Bearings When Contact Occurs
Journal of Tribology, 2001Co-Authors: M. Anaya-dufresne, G. B. SinclairAbstract:The various existing forms of Reynolds equation are known to yield pressure fields which are unbounded and nonphysical when contact occurs. With a view to developing a Reynolds equation that is suitable for contact, here we revisit Taylor's plate scraping problem for incompressible flow. This problem has an infinite pressure where the scraper contacts the plate. By suitably modifying Maxwell's slip condition, the scraping problem can be reformulated so as to lead to finite pressures. This is shown locally via asymptotics, and globally via convergence checks. The approach looks sufficiently promising to consider the further development needed for the compressible flow present in Gas Lubricated Bearings.
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On the Breakdown Under Contact Conditions of Reynolds Equation for Gas Lubricated Bearings
Journal of Tribology, 1997Co-Authors: M. Anaya-dufresne, G. B. SinclairAbstract:For the analysis of Gas Lubricated Bearings, Reynolds equation is available in a number of forms-the original version, first-order modified, second-order modified, one-and-a-half order modified, and Boltzmann-Reynolds. All of these variants are asymptotically examined for instances in which local contact occurs in a bearing. These asymptotics serve to identify the order of the respective singularities in pressures, and thus imply the possible consequences of using a particular version of Reynolds equation in the presence of contact.
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Some exact solutions of Reynolds equation
Journal of Tribology, 1995Co-Authors: M. Anaya-dufresne, G. B. SinclairAbstract:In order to check the numerical analysis of Reynolds equation for Gas Lubricated Bearings, it is desirable to have available exact analytical solutions. This note outlines the construction of some exact, two-dimensional, transient solutions for this purpose
Yongfang Zhang - One of the best experts on this subject based on the ideXlab platform.
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Nonlinear dynamic analysis of a rotor system with fixed-tilting-pad self-acting Gas-Lubricated Bearings support
Nonlinear Dynamics, 2012Co-Authors: Yongfang Zhang, Xiaolei Shi, Weimin WangAbstract:Based on the nonlinear theory, the unbalanced responses of a fixed-tilting-pad Gas-Lubricated journal bearing-rigid rotor system are investigated. A time-dependent mathematical model is established to describe the pressure distribution of Gas-Lubricated journal bearing with nonlinearity. The rigid rotor supported by a fixed-tilting-pad self-acting Gas-Lubricated journal bearing is modeled. The differential transformation method has been employed to solve the time-dependent Gas-Lubricated Reynolds equation, and the dynamic motion equation has been solved by the direct integral method. The unbalanced responses of the rotor system supported by fixed-tilting-pad Gas-Lubricated journal Bearings are analyzed by the orbit diagram, Poincare map, time series, and spectrum diagram. The numerical results reveal periodic, period-3, and quasiperiodic motions of nonlinear behaviors of the system. Finally, the effects of pivot ratio and preload coefficient on the nonlinear dynamic characteristics of the fixed-tilting-pad self-acting Gas-Lubricated journal bearing-rotor system are investigated.
