Effect of Side Feed Pressurization on the Dynamic Performance of Gas Foil Bearings

2007 ◽  
Author(s):  
Luis San Andre´s ◽  
Tae Ho Kim
Keyword(s):  
Gas Turbines ◽  
Gas Flow ◽  
Dynamic Performance ◽  
Mechanical Efficiency ◽  
System Stability ◽  
Remarkable Effect ◽  
Foil Bearings ◽  
Feed Pressure ◽  
Side Pressure ◽  
The Difference

Oil-free micro turbomachinery implementing gas foil bearings (GFBs) has improved mechanical efficiency and reliability. Adequate thermal management for operation in high temperature environments is an issue of importance in applications such as in gas turbines and turbochargers. GFBs often need a cooling gas flow, axially fed through one end of the bearing, to transport the heat conducted from a hot turbine, for example. Side gas pressurization, however, has a paramount effect on reducing amplitudes of motion, synchronous and subsynchronous. Presently, shaft motion measurements in a test rotor supported on GFBs show this remarkable effect. A computational gas film model implementing the evolution of gas circumferential flow velocity as a function of the imposed side pressure is advanced. Predicted direct stiffnesses and damping coefficients for the test GFB increase as the magnitude of feed pressure raises, while the difference in cross-coupled stiffnesses, directly related to rotor-bearing system stability, decreases. Predictions of threshold speed of instability and whirl frequency ratio are in close agreement with the measurements.

Effect of Side Feed Pressurization on the Dynamic Performance of Gas Foil Bearings: A Model Anchored to Test Data

2008 ◽  
Author(s):  
Tae Ho Kim ◽  
Luis San Andre´s
Keyword(s):  
Test Data ◽  
High Speed ◽  
Gas Flow ◽  
Dynamic Performance ◽  
Rotor Speed ◽  
Mass Distributions ◽  
Foil Bearings ◽  
Feed Pressure ◽  
Run Up ◽  
Forced Cooling

Comprehensive modeling of gas foil bearings (GFBs) anchored to reliable test data will enable the widespread usage of these bearings into novel high speed turbomachinery applications. GFBs often need a forced cooling gas flow, axially fed through one end of the bearing, for adequate thermal management. The paper presents rotordynamic response measurements on a rigid rotor supported on GFBs during rotor speed run-up and coastdown tests with the GFBs supplied with increasing feed gas pressures to 2.8 bar. Rotor speed run-up tests to 35 krpm show that bearing end side feed gas pressurization delays the onset speed of rotor subsynchronous whirl motions. The test data validate closely predictions of the threshold speed of instability and whirl frequency ratio derived from a GFB model that implements the axial evolution of gas circumferential flow velocity as a function of the imposed side feed pressure. Rotor speed coastdown tests from 25 krpm with a low feed pressure of 0.35 bar evidences a nearly linear synchronous rotor response for small and moderately large imbalance mass distributions. A structural FE rotordynamics model integrates linearized synchronous speed GFB force coefficients and predicts synchronous responses, amplitude and phase angle, agreeing with the test data. The analysis and measurements demonstrate the profound effect of end side, feed gas pressurization on the rotordynamic performance of GFBs.

Effect of Side Feed Pressurization on the Dynamic Performance of Gas Foil Bearings: A Model Anchored to Test Data

2008 ◽  
Vol 131 (1) ◽  
Author(s):  
Tae Ho Kim ◽  
Luis San Andrés
Keyword(s):  
Test Data ◽  
High Speed ◽  
Gas Flow ◽  
Dynamic Performance ◽  
Rotor Speed ◽  
Mass Distributions ◽  
Foil Bearings ◽  
Feed Pressure ◽  
Run Up ◽  
Phase Angles

Comprehensive modeling of gas foil bearings (GFBs) anchored to reliable test data will enable the widespread usage of these bearings into novel high speed turbomachinery applications. GFBs often need a forced cooling gas flow, axially fed through one end of the bearing, for adequate thermal management. This paper presents rotordynamic response measurements on a rigid rotor supported on GFBs during rotor speed run-up and coastdown tests with the GFBs supplied with increasing feed gas pressures to 2.8bars. Rotor speed run-up tests to 35krpm show that the bearing end side feed gas pressurization delays the onset speed of rotor subsynchronous whirl motions. The test data validate closely the predictions of the threshold speed of instability and the whirl frequency ratio derived from a GFB model that implements the axial evolution of gas circumferential flow velocity as a function of the imposed side feed pressure. Rotor speed coastdown tests from 25krpm with a low feed pressure of 0.35bar evidence a nearly linear synchronous rotor response for small and moderately large imbalance mass distributions. A structural finite element rotordynamics model integrates linearized synchronous speed GFB force coefficients and predicts synchronous responses, amplitude, and phase angles, agreeing with the test data. The analysis and measurements demonstrate the profound effect of the end side feed gas pressurization on the rotordynamic performance of GFBs.

An experimental investigation of a microturbine simulated rotor supported on multileaf gas foil bearings with backing bump foils

2017 ◽  
Vol 232 (9) ◽  
pp. 1169-1180 ◽  
Author(s):  
Bo Zhang ◽  
Shemiao Qi ◽  
Sheng Feng ◽  
Haipeng Geng ◽  
Yanhua Sun ◽  
...  
Keyword(s):  
High Speed ◽  
Preliminary Test ◽  
Journal Bearings ◽  
Rotating Machinery ◽  
System Stability ◽  
Test Rig ◽  
Thrust Bearings ◽  
Foil Bearings ◽  
Simulated System ◽  
First Time

Two multileaf gas foil journal bearings with backing bump foils and one set of gas foil thrust bearings were designed, fabricated, and used in a 100 kW class microturbine simulated rotor system to ensure stability of the system. Meanwhile, a preliminary test rig had been built to verify the simulated system stability. The rotor synchronous and subsynchronous responses were well controlled by using of the gas foil bearings. It is on the multileaf gas foil bearings with backing bump foils that the test was conducted and verified for the first time in open literatures. The success in the experiments shows that the design and fabrication of the rotor and the gas foil bearings can provide a useful guide to the development of the advanced high speed rotating machinery.

scholarly journals Methods for the Calculation of Thermoacoustic Stability Margins and Monte Carlo-Free Uncertainty Quantification

2017 ◽  
Author(s):  
Georg A. Mensah ◽  
Luca Magri ◽  
Jonas P. Moeck
Keyword(s):  
Monte Carlo ◽  
Factor Analysis ◽  
Risk Factor ◽  
Uncertainty Quantification ◽  
Frequency Domain ◽  
Gas Turbines ◽  
Network Models ◽  
System Stability ◽  
Risk Factor Analysis ◽  
Model Parameters

Thermoacoustic instabilities are a major threat for modern gas turbines. Frequency-domain based stability methods, such as network models and Helmholtz solvers, are common design tools because they are fast compared to compressible CFD computations. Frequency-domain approaches result in an eigenvalue problem, which is nonlinear with respect to the eigenvalue. Nonlinear functions of the frequency are, for example, the n–τ model, impedance boundary conditions, etc. Thus, the influence of the relevant parameters on mode stability is only given implicitly. Small changes in some model parameters, which are obtained by experiments with some uncertainty, may have a great impact on stability. The assessment of how parameter uncertainties propagate to system stability is therefore crucial for safe gas turbine operation. This question is addressed by uncertainty quantification. A common strategy for uncertainty quantification in thermoacoustics is risk factor analysis. It quantifies the uncertainty of a set of parameters in terms of the probability of a mode to become unstable. One general challenge regarding uncertainty quantification is the sheer number of uncertain parameter combinations to be quantified. For instance, uncertain parameters in an annular combustor might be the equivalence ratio, convection times, geometrical parameters, boundary impedances, flame response model parameters etc. Assessing also the influence of all possible combinations of these parameters on the risk factor is a numerically very costly task. A new and fast way to obtain algebraic parameter models in order to tackle the implicit nature of the eigenfrequency problem is using adjoint perturbation theory. Though adjoint perturbation methods were recently applied to accelerate the risk factor analysis, its potential to improve the theory has not yet been fully exploited. This paper aims to further utilize adjoint methods for the quantification of uncertainties. This analytical method avoids the usual random Monte Carlo simulations, making it particularly attractive for industrial purposes. Using network models and the open-source Helmholtz solver PyHoltz it is also discussed how to apply the method with standard modeling techniques. The theory is exemplified based on a simple ducted flame and a combustor of EM2C laboratory for which experimental validation is available.

Fanno Design of Blow-Off Lines in Heavy Duty Gas Turbine

2013 ◽  
Author(s):  
Marco Cioffi ◽  
Enrico Puppo ◽  
Andrea Silingardi
Keyword(s):  
Gas Turbines ◽  
Gas Flow ◽  
Initial Conditions ◽  
Three Dimensional ◽  
Design Procedure ◽  
Flow Equation ◽  
Heavy Duty ◽  
Cross Sectional ◽  
Pipe Length ◽  
Choked Flow

In typical heavy duty gas turbines the multistage axial compressor is provided with anti-surge pipelines equipped with on-off valves (blow-off lines), to avoid dangerous flow instabilities during start-ups and shut-downs. Blow-off lines show some very peculiar phenomena and somewhat challenging fluid dynamics, which require a deeper regard. In this paper the blow-off lines in axial gas turbines are analyzed by adopting an adiabatic quasi-unidimensional model of the gas flow through a pipe with a constant cross-sectional area and involving geometrical singularities (Fanno flow). The determination of the Fanno limit, on the basis of the flow equation and the second principle of thermodynamics, shows the existence of a critical pipe length which is a function of the pipe parameters and the initial conditions: for a length greater than this maximum one, the model requires a mass-flow reduction. In addition, in the presence of a regulating valve, so-called multi-choked flow can arise. The semi-analytical model has been implemented and the results have been compared with a three-dimensional CFD analysis and cross-checked with available field data, showing a good agreement. The Fanno model has been applied for the analysis of some of the actual machines in the Ansaldo Energia fleet under different working conditions. The Fanno tool will be part of the design procedure of new machines. In addition it will define related experimental activities.

scholarly journals ANALYSIS OF SMES CREDIT RESTRUCTURING POLICY IN ECONOMIC RECOVERY DURING THE COVID-19 PANDEMIC

2021 ◽  
Vol 5 (2) ◽  
pp. 405
Author(s):  
Lussi Agustin ◽  
Moh. Yusron Solikin ◽  
Zunairoh .
Keyword(s):  
Financial Services ◽  
Global Economy ◽  
Empirical Studies ◽  
System Stability ◽  
Economic Recovery ◽  
Top Down ◽  
The Difference ◽  
Almost All ◽  
Industry Sectors ◽  
The Impact

Penelitian ini bertujuan untuk menganalisis seberapa maksimal proses kebijakan retrukturisasi Kredit UMKM dalam Pemulihan Ekonomi di Masa Pandemi Covid-19. Kondisi perekonomian global sedang mengalami goncangan hebat akibat mewabahnya Covid-19. Dampak dari pandemic ini sangat mempengaruhi segala aspek terutama pada kondisi Kesehatan dan perekonomian suatu negara, tidak terkecuali Indonesia. Secara keseluruhan, hampir semua sektor industry mengalami goncangan dan tidak terkecuali sektor UMKM. Maka dari itu dikeluarkanlah kebijakan retrukturisasi Kredit UMKM guna mendorong optimalisasi fungsi intermediasi pada perbankan dan menjaga stabilitas sistem keuangan serta mendukung pertumbuhan perekonomian. Program restrukturisasi kredit menjadi program dari OJK yang dapat diterapkan oleh perbankan kepada UMKM. Metode yang digunakan dalam penelitian ini adalah metode kualitatif dengan menggunakan studi empiris dari penelitian terdahulu serta peraturan-peraturan terkait dengan restrukturisasi kredit yang dikeluarkan oleh Otoritas Jasa Keuangan. Hasil penelitian ini menunjukkan bahwa implementasi kebijakan restrukturisai kredit bagi UMKM sudah berjalan dan digunakan oleh para pelaku UMKM. Kemudian berdasarkan implementasinya kebijakan ini merupakan kebijakan top-down dimana memerlukan banyak Lembaga untuk bekerja sama dan keputusan berasal dari Peraturan pemerintah baru di teruskan ke Lembaga-lembaga lain di bawahnya hingga informasinya sampai dan bisa dirasakan oleh para UMKM.  This research aims to analyze the policy of restructuring SMEs Credit in Economic Recovery during the Covid-19 Pandemic. The global economy is experiencing severe shocks due to the outbreak of Covid-19. The impact of this pandemic greatly affects all aspects, especially on the health and economic condition of a country, not least Indonesia. Overall, almost all industry sectors are experiencing shocks and are no exception to the SMEs sector. Therefore, the policy of restructuring SMEs Credit was issued to encourage optimization of intermediation function in banking and maintain the financial system stability and support economic growth. Credit restructuring program becomes a program from OJK that can be applied by banks to SMEs. The method used in this research is a qualitative method using empirical studies from previous research as well as regulations related to credit restructuring issued by the Financial Services Authority. The results of this research show that the implementation of credit restructuring policy for SMEs is already running and used by SMEs. Then based on the difference in implementation of this policy is a top-down policy that requires many Institutions to cooperate and decisions derived from the new government regulations are forwarded to other institutions under it until the information reaches and can be felt by SMEs.

scholarly journals The gas flow pattern through small size Resistive Plate Chambers with 2 mm gap

2021 ◽  
Vol 16 (11) ◽  
pp. P11022
Author(s):  
Y. Pezeshkian ◽  
A. Kiyoumarsioskouei ◽  
M. Ahmadpouri ◽  
G. Ghorbani
Keyword(s):  
Gas Flow ◽  
Fluid Dynamic ◽  
Gas Flow Rate ◽  
Argon Gas ◽  
Dynamic Methods ◽  
Gas System ◽  
Gas Molecules ◽  
Simulation Results ◽  
Resistive Plate Chambers ◽  
The Difference

Abstract A prototype of a single-gap glass Resistive Plate Chamber (RPC) is constructed by the authors. To find the requirements for better operation of the detector's gas system, we have simulated the flow of the Argon gas through the detector by using computational fluid dynamic methods. Simulations show that the pressure inside the chamber linearly depends on the gas flow rate and the chamber's output hose length. The simulation results were compatible with experiments. We have found that the pressure-driven speed of the gas molecules is two orders of magnitude larger in the inlet and outlet regions than the blocked corners of a 14 × 14 cm2 chamber, and most likely the difference in speed is higher for larger detectors and different geometries.

scholarly journals Influence of Temperature Effect on the Static and Dynamic Performance of Gas-Lubricated Microbearings

Micromachines ◽  
2020 ◽  
Vol 11 (8) ◽  
pp. 716
Author(s):  
Liangliang Li ◽  
Zhufeng Liu ◽  
Chongyu Wang ◽  
Yonghui Xie
Keyword(s):  
High Speed ◽  
Load Capacity ◽  
Dynamic Performance ◽  
Operating Environment ◽  
Low Friction ◽  
Operating Stability ◽  
Comprehensive Performance ◽  
Different Temperatures ◽  
Dynamic Performances ◽  
The Difference

Gas-lubricated microbearings are widely applied in multiple fields due to their advantages of high-speed, low friction level and other features. The operating environment of microbearings is complex, and the difference of temperature has an important influence on their comprehensive performance. In this investigation, FEM (finite element method) is employed to investigate the static, dynamic and limit characteristics of microbearings lubricated by different kinds of gas at different temperatures. The results show that the rise of temperature leads to the decline of equivalent viscosity of gas, which weakens the load capacity of microbearings, and furthermore, affects the operating stability of microbearings. The dynamic performances of microbearings at different temperatures are very different, and the two dynamic limit characteristics are more sensitive to temperature when it changes.

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