Steady Characteristics of High-Speed Micro-Gas Journal Bearings With Different Gaseous Lubricants and Extreme Temperature Difference

2016 ◽  
Vol 139 (2) ◽  
Author(s):  
Xueqing Zhang ◽  
Qinghua Chen ◽  
Juanfang Liu
Keyword(s):  
High Temperature ◽  
Temperature Difference ◽  
Gas Turbines ◽  
High Speed ◽  
Load Capacity ◽  
Axial Direction ◽  
Operating Conditions ◽  
Thermal Creep ◽  
Large Temperature ◽  
The Stability

High-speed micro-gas journal bearing is one of the essential components of micro-gas turbines. As for the operating conditions of bearings, the high-speed, high-temperature, ultra-high temperature difference along the axial direction and the species of gaseous lubricants are extremely essential to be taken into account, and the effects of these factors are examined in this paper. The first-order modified Reynolds equation including the thermal creep, which results from the extremely large temperature gradient along the axial direction, is first derived and coupled with the simplified energy equation to investigate the steady hydrodynamic characteristics of the micro-gas bearings. Under the isothermal condition, it is found that CO2 can not only improve the stability of bearings but also generate a relatively higher load capacity by some comparisons. Thus, CO2 is chosen as the lubricant to further explore the influence of thermal creep. As the rotation speed and eccentricity ratio change, the thermal creep hardly has any effect on the gas film pressure. However, the shorter bearing length can augment the thermal creep. Compared with the cases without the thermal creep, the thermal creep could remarkably destroy the stability of gas bearing, but it might slightly enhance the load capacity.

Design Characteristics of an Aerodynamic Foil Bearing With Adaptable Bore Clearance

2018 ◽  
Author(s):  
Hossein Sadri ◽  
Henning Schlums ◽  
Michael Sinapius
Keyword(s):  
Gas Turbines ◽  
High Speed ◽  
Load Capacity ◽  
Functional Model ◽  
Operating Conditions ◽  
Radial Clearance ◽  
Static Properties ◽  
Advantages And Disadvantages ◽  
Aerodynamic Pressure ◽  
Foil Bearing

Aerodynamic foil bearings are suitable to support light, high-speed rotors under extreme operating conditions such as very low or very high temperatures, e.g. in cooling turbines, small gas turbines or exhaust gas turbochargers. The required bearing load capacity is generated by an aerodynamic pressure build-up in the corresponding lubrication gap. Due to the high dependence of the bearing performance on the bore geometry, the rotordynamic behavior (e.g. bearing stability) and static properties (e.g. load capacity) as a function of radial clearance and hydrodynamic preload are one of the main points of interest in recent studies. The outcome of both the experimental and the numerical investigations show the advantages and disadvantages of the various configurations of the bearing bore in different operating conditions. These observations lead to the basic idea of an adaptive air foil bearing (AAFB) in which, depending on the operating conditions, the bearing bore contour is changed by means of piezoelectric actuators applied to the compliant supporting shell. Similar to other shape morphing approaches, optimization with regard to various components of the mechanism is the next step in the design process after targeting the design pattern. This paper concentrates on an AAFB as an efficient approach to actively shape the contour of the bore clearance in a 3-pad bearing. Numerous FEM analyses of a functional model for an AAFB in addition to the experimental efforts reveal the main concerns of the design. Finally, the result of this study is a working graph for the AAFB under various loading conditions while operating with different input voltages of the actuators.

Influence of Carrier Air Preheating on Autoignition of Inline-Injected Hydrogen-Nitrogen Mixtures in Vitiated Air of High Temperature

2017 ◽  
Author(s):  
Christoph A. Schmalhofer ◽  
Peter Griebel ◽  
Manfred Aigner
Keyword(s):  
High Temperature ◽  
Gas Turbine ◽  
Gas Turbines ◽  
High Speed ◽  
Spatial Development ◽  
Design Guidelines ◽  
Operating Conditions ◽  
High Speed Imaging ◽  
Temporal And Spatial ◽  
Fuel Mixtures

Gas turbines will play a significant role in future power generation systems because they provide peak capacity due to their fast start-up capability and high operational flexibility. However, in order to meet the COP 21 goals, de-carbonization of as turbine fuels is required. Compared to natural gas operation, autoignition and flashback risks in gas turbines operated on hydrogen-rich fuels are higher which has to be taken into account for a proper gas turbine design. From investigations of these phenomena at relevant operating conditions with appropriate measurement techniques, e.g. high-speed imaging, the understanding of the non-stationary processes occurring during autoignition can be improved and design guidelines for a safe and reliable gas turbine operation can be derived. The present study investigates the influences of elevated carrier-air preheating temperatures and hydrogen fuel volume fractions on autoignition at hot gas temperatures higher than 1100 K and pressures of 15 bar. An in-line co-flow injector is used to inject the hydrogen-nitrogen fuel mixtures. The formation, temporal and spatial development of autoignition kernels at high-temperature vitiated air conditions, e.g. relevant to reheat combustor operation, are studied. The experiments were conducted in an optically accessible mixing section of a generic reheat combustor. The hydrogen-nitrogen fuel mixtures of up to 70 vol. % hydrogen are injected in-line into the mixing section along with the carrier-air which was preheated to temperatures between 303 K and 703 K. High-speed imaging was used to detect the autoignition kernels and their temporal and spatial development from luminescence signals. Particle Image Velocimetry measurements were conducted to obtain the velocity distribution in the mixing section at autoignition conditions. The influences of vitiated air temperatures and carrier preheating temperatures on autoignition and flame stabilisation limits are shown, alongside the spatial distribution of different types of autoignition kernels, developing at different stages of the autoignition process. The development of autoignition kernels could be linked to the shear layer development derived from global experimental conditions.

scholarly journals The Influence of Carrier Air Preheating on Autoignition of Inline-Injected Hydrogen–Nitrogen Mixtures in Vitiated Air of High Temperature

2017 ◽  
Vol 140 (3) ◽  
Author(s):  
Christoph A. Schmalhofer ◽  
Peter Griebel ◽  
Manfred Aigner
Keyword(s):  
Hydrogen Content ◽  
Gas Turbines ◽  
High Speed ◽  
Flame Stabilization ◽  
Operating Conditions ◽  
Promoting Effect ◽  
Experimental Conditions ◽  
Lean Premixed Combustion ◽  
Image Velocimetry ◽  
Fuel Mixtures

The use of highly reactive hydrogen-rich fuels in lean premixed combustion systems strongly affects the operability of stationary gas turbines (GT) resulting in higher autoignition and flashback risks. The present study investigates the autoignition behavior and ignition kernel evolution of hydrogen–nitrogen fuel mixtures in an inline co-flow injector configuration at relevant reheat combustor operating conditions. High-speed luminosity and particle image velocimetry (PIV) measurements in an optically accessible reheat combustor are employed. Autoignition and flame stabilization limits strongly depend on temperatures of vitiated air and carrier preheating. Higher hydrogen content significantly promotes the formation and development of different types of autoignition kernels: More autoignition kernels evolve with higher hydrogen content showing the promoting effect of equivalence ratio on local ignition events. Autoignition kernels develop downstream a certain distance from the injector, indicating the influence of ignition delay on kernel development. The development of autoignition kernels is linked to the shear layer development derived from global experimental conditions.

Prototype Design of a High-Speed Viscous Air Spindle

2008 ◽  
Author(s):  
Guido M. J. Delhaes ◽  
Anton van Beek ◽  
Ron A. J. van Ostayen ◽  
Robert H. Munnig Schmidt
Keyword(s):  
High Speed ◽  
Load Capacity ◽  
Axial Direction ◽  
Cylindrical Part ◽  
Traction Forces ◽  
Micro Cutting ◽  
Tool Holder ◽  
Air Spindle ◽  
Prototype Design

In this paper an innovative air driven spindle for micro cutting applications is presented. The spindle uses a viscous traction concept which has the advantage that the viscous traction forces can act directly on the cylindrical part of the tool, which makes the tool-holder redundant. Furthermore, the tool can be actuated in the axial direction within the housing. In this paper the concept of the viscous turbine, a design of a prototype spindle along with the traction and load-capacity of the spindle are discussed.

scholarly journals Thin Gas Film Isothermal Condensation in Aerodynamic Bearings

2019 ◽  
Vol 141 (11) ◽  
Author(s):  
Eliott Guenat ◽  
Jürg Schiffmann
Keyword(s):  
High Speed ◽  
Waste Heat ◽  
Load Capacity ◽  
Saturation Pressure ◽  
Operating Conditions ◽  
Fluid Film ◽  
Small Scale ◽  
Vapor Compression ◽  
Density Profiles ◽  
Film Pressure

Abstract High-speed small-scale turbomachinery for waste heat recovery and vapor compression cycles is typically supported on gas-lubricated bearings operating close to the saturation conditions of the lubricant. Under particular conditions, the gas film might locally reach the saturation pressure with potentially hazardous effects on the performance of the gas bearing. The present work introduces a model based on the Reynolds equation and the development of cavitation modeling in liquid-lubricated bearings for condensing gas bearings. The effect of condensation on load capacity and pressure and density profiles is investigated for two one-dimensional bearing geometries (parabolic and Rayleigh step) and varying operating conditions. The results suggest that the load capacity is generally negatively affected if condensation occurs. An experimental setup consisting of a Rayleigh-step gas journal bearing with pressure taps to measure the local fluid film pressure is presented and operated in R245fa in near-saturated conditions. The comparison between the evolution of the fluid film pressure under perfect gas and near saturation conditions clearly suggests the occurrence of condensation in the fluid film. These results are corroborated by the very good agreement with the model prediction.

Double-diffusive instabilities in a vertical slot

1999 ◽  
Vol 392 ◽  
pp. 213-232 ◽  
Author(s):  
OLIVER S. KERR ◽  
KIT YEE TANG
Keyword(s):  
Temperature Difference ◽  
Salinity Gradient ◽  
Stability Boundary ◽  
Large Temperature ◽  
Vertical Slot ◽  
Stability And Instability ◽  
Heat Diffusivity ◽  
Prandtl Numbers ◽  
The Stability ◽  
Double Diffusive

A fluid stably stratified by a salinity gradient and enclosed between two vertical boundaries can become unstable when it is subjected to a temperature difference between the walls. The linear stability of such a fluid in a vertical slot is investigated. Errors in earlier results are found, confirming recent results of Young & Rosner (1998). Four different asymptotic regimes on the stability boundary are identified. One of these, the limit of a strong salinity gradient, has previously been analysed. The analyses of the separate asymptotic limits of weak salinity gradient, large temperature difference and small wavenumber are also given. These four cases make up much of the total boundary between stability and instability for double-diffusive instabilities in a vertical slot, and so most of this boundary can be mapped out for general Prandtl numbers and salt/heat diffusivity ratios using these results.

Advancement in Heated Spin Testing Technologies

2013 ◽  
Author(s):  
Hiroaki Endo ◽  
Robert Wetherbee ◽  
Nikhil Kaushal
Keyword(s):  
High Temperature ◽  
Gas Turbine ◽  
Material Properties ◽  
Gas Turbines ◽  
Multiple Scales ◽  
Thermal Conditions ◽  
Complex Stress ◽  
Operating Conditions ◽  
Mechanical Cycling ◽  
Testing Techniques

An ever more rapidly accelerating trend toward pursuing more efficient gas turbines pushes the engines to hotter and more arduous operating conditions. This trend drives the need for new materials, coatings and associated modeling and testing techniques required to evaluate new component design in high temperature environments and complex stress conditions. This paper will present the recent advances in spin testing techniques that are capable of creating complex stress and thermal conditions, which more closely represent “engine like” conditions. The data from the tests will also become essential references that support the effort in Integrated Computational Materials Engineering (ICME) and in the advances in rotor design and lifing analysis models. Future innovation in aerospace products is critically depended on simultaneous engineering of material properties, product design, and manufacturing processes. ICME is an emerging discipline with an approach to design products, the materials that comprise them, and their associated materials processing methods by linking materials models at multiple scales (Structural, Macro, Meso, Micro, Nano, etc). The focus of the ICME is on the materials; understanding how processes produce material structures, how those structures give rise to material properties, and how to select and/or engineer materials for a given application [34]. The use of advanced high temperature spin testing technologies, including thermal gradient and thermo-mechanical cycling capabilities, combined with the innovative use of modern sensors and instrumentation methods, enables the examination of gas turbine discs and blades under the thermal and the mechanical loads that are more relevant to the conditions of the problematic damages occurring in modern gas turbine engines.

Investigation on Flat-Fan Spray Characterization in High-Speed Air Coflow for Gas Turbine Online Water Washing Application

2021 ◽  
Author(s):  
Kiran Kumar ◽  
Vasudev Chaudhari ◽  
Srikrishna Sahu ◽  
Ravindra G. Devi
Keyword(s):  
Droplet Size ◽  
Gas Turbines ◽  
High Speed ◽  
Numerical Models ◽  
Cone Angle ◽  
Operating Conditions ◽  
Spray Characteristics ◽  
Spray Cone ◽  
Water Washing ◽  
Spray Characterization

Abstract Fouling in compressor blades due to dirt deposition is a major issue in land-based gas turbines as it impedes the compressor performance and degrades the overall engine efficiency. The online water washing approach is an effective alternate for early-stage compressor blade cleaning and to optimize the time span between offline washing and peak availability. In such case, typically a series of flat-fan nozzles are used at the engine bell mouth to inject water sprays into the inflowing air. However, optimizing the injector operating conditions is not a straightforward task mainly due to the tradeoff between blade cleaning effectiveness and material erosion. In this context, the knowledge on spray characteristics prior to blade impingement play a vital role, and the experimental spray characterization is crucial not only to understand the basic process but also to validate numerical models and simulations. The present paper investigates spray characteristics in a single flat-fan nozzle operated in the presence of a coflowing air within a wind-tunnel. A parametric investigation is carried out using different air flow velocity in the tunnel and inlet water temperature, while the liquid flow rate was maintained constant. The spray cone angle and liquid breakup length are measured using back-lit photography. The high-speed shadowgraphy technique is used for capturing the droplet images downstream of the injector exit. The images are processed following depth-of-filed correction to measure droplet size distribution. Droplet velocity is measured by the particle tracking velocimetry (PTV) technique. As both droplet size and velocity are known, the cross-stream evolution of local droplet mass and momentum flux are obtained at different axial locations which form the basis for studying the effectiveness of the blade cleaning process due to droplet impingement on a coupon coated with foulant of known mass.

Review of the Study on Load Capacity of Oil-Film Bearings

2014 ◽  
Vol 900 ◽  
pp. 405-409
Author(s):  
Xiang Jun Yu ◽  
Zuo Xin Li ◽  
Ke Nan Shen ◽  
Shuang You ◽  
An Jun Wu
Keyword(s):  
Dynamic Simulation ◽  
Experimental Test ◽  
Load Capacity ◽  
Operating Conditions ◽  
Mechanical Transmission ◽  
Paper Briefly ◽  
Scaled Model ◽  
Oil Film ◽  
Depth Study ◽  
The Stability

The oil-film bearings are widely used in mechanical transmission due to the good performance. In normal operating conditions, the journal and bearing shell are separated by the oil film, which contributes to the reduction of wear. And the stability and reliability of oil film has a great effect on load capacity. The paper briefly introduces research methods of the load capacity of oil-film bearings and points out some aspects of large oil-film bearings for in-depth study. Then combining dynamic simulation with experimental test on the scaled model of whole machine, a dynamic research idea is presented for large oil-film bearings.

Effect of misalignment and rarefaction effect on the comprehensive characteristic of MEMS gas bearing

2020 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Liangliang Li ◽  
Yonghui Xie
Keyword(s):  
Peer Review ◽  
High Speed ◽  
Rarefied Gas ◽  
Load Capacity ◽  
Content Type ◽  
Rarefaction Effect ◽  
Comprehensive Performance ◽  
Static Performance ◽  
The Stability ◽  
Gas Bearing

Purpose Owing to the development of the smaller-sized rotational machinery, the demand for the high-speed and low-resistance gas bearing increases rapidly. The research of micro gas bearing in the condition of rarefied gas state is still not satisfied. Therefore, the purpose of this paper is to present a numerical investigation of the effect of misalignment and rarefaction effect on the comprehensive performance of micro-electrical-mechanical system (MEMS) gas bearing. Design/methodology/approach The Fukui and Kaneko model is expanded to 2D solution domain to describe the flow field parameters. The finite element method is used to discretize the equation. Newton–Raphson method is used to solve the nonlinear equations for the static performance of gas bearing, and partial deviation method is adopted for the solution of dynamic equations. Findings The static and dynamic characteristics of MEMS gas bearing are calculated, and the comparison is made to study the influence of rarefaction effect and misalignment. The results show that the rarefaction effect will decrease bearing load capacity compared with traditional solution of Reynolds equation, and the misalignment will reduce the stability of bearing. The influence of misalignment on gas film thickness is also analyzed in this paper. Originality/value The investigation of this paper emerges the change regularity of comprehensive performance of MEMS gas bearing considering rarefaction effect and misalignment, which provides a reference for the actual manufacturing of MEMS gas bearing and for the safety operation of micro dynamic machinery. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-01-2020-0023/

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