Linear Growth Rate Estimation From Dynamics and Statistics of Acoustic Signal Envelope in Turbulent Combustors

2016 ◽  
Vol 139 (4) ◽  
Author(s):  
Nicolas Noiray
Keyword(s):  
Gas Turbine ◽  
Acoustic Signal ◽  
Growth Rates ◽  
Linear Growth ◽  
Dynamic Pressure ◽  
Linear Growth Rate ◽  
Case Scenario ◽  
Major Step ◽  
Worst Case ◽  
Signal Envelope

Considerable research and development efforts are required to meet the targets of future gas turbine technologies in terms of performance, emissions, and operational flexibility. One of the recurring problems is the constructive coupling between flames and combustor's acoustics. These thermoacoustic interactions can cause high-amplitude dynamic pressure limit cycles, which reduce the lifetime of the hot gas path parts or in the worst-case scenario destroy these mechanical components as a result of a sudden catastrophic event. It is shown in this paper that the dynamics and the statistics of the acoustic signal envelope can be used to identify the linear growth rates hidden behind the observed pulsations, and the results are validated against numerical simulations. This is a major step forward and it will contribute to the development of future gas turbine combustors, because the knowledge of these linear growth rates is essential to develop robust active and passive systems to control these combustion instabilities.

Linear Growth Rate Estimation From Dynamics and Statistics of Acoustic Signal Envelope in Turbulent Combustors

2016 ◽  
Author(s):  
Nicolas Noiray
Keyword(s):  
Gas Turbine ◽  
Acoustic Signal ◽  
Growth Rates ◽  
Linear Growth ◽  
Dynamic Pressure ◽  
Linear Growth Rate ◽  
Case Scenario ◽  
Major Step ◽  
Worst Case ◽  
Signal Envelope

Considerable research and development efforts are required to meet the targets of future gas turbine technologies in terms of performance, emissions and operational flexibility. One of the recurring problem is the constructive coupling between flames and combustor’s acoustics. These thermoacoustic interactions can cause high amplitude dynamic pressure limit cycles, which reduce the lifetime of the hot-gas-path parts or in the worst case scenario destroy these mechanical components as a result of a sudden catastrophic event. It is shown in this paper that the dynamics and the statistics of the acoustic signal envelope can be used to identify the linear growth rates hidden behind the observed pulsations, and the results are validated against numerical simulations. This is a major step forward and it will contribute to the development of future gas turbine combustors, because the knowledge of these linear growth rates is essential to develop robust active and passive systems to control these combustion instabilities.

Analysis of Azimuthal Thermoacoustic Modes in Annular Gas Turbine Combustion Chambers

2014 ◽  
Author(s):  
Mirko Bothien ◽  
Nicolas Noiray ◽  
Bruno Schuermans
Keyword(s):  
Gas Turbine ◽  
Network Model ◽  
Growth Rates ◽  
Linear Growth ◽  
Flame Temperature ◽  
Full Scale ◽  
Analytical Models ◽  
Linear Growth Rate ◽  
Combustion Chambers ◽  
Engine Operation

Modern gas turbine combustors operating in lean-premixed mode are prone to thermoacoustic instabilities. In annular combustion chambers, usually azimuthal acoustic modes are the critical ones interacting with the flame. In case of constructive interference, high amplitude oscillations might result. In this paper, the azimuthal acoustic field of a full-scale engine is investigated in detail. The analyses are based on measurements in a full-scale gas turbine, analytical models to derive the system dynamics, as well as simulations performed with an in-house 3d nonlinear network model. It is shown that the network model is able to reproduce the behaviour observed in the engine. Spectra, linear growth rates, as well as the statistics of the system’s dynamics can be predicted. A previously introduced algorithm is used to extract linear growth rates from engine and model time domain data. The method’s accuracy is confirmed by comparison of the routine’s results to analytically determined growth rates from the network model. The network model is also used to derive a burner staging configuration resulting in the decrease of linear growth rate and thus an increase of engine operation regime; model predictions are verified by full-scale engine measurements. A thorough investigation of the azimuthal modes statistics is performed. Additionally, the network model is used to show that an unfavorable flame temperature distribution with an amplitude of merely 1% of the mean flame temperature can change the azimuthal mode from dominantly rotating to dominantly standing. This is predicted by the network model that only takes into account flame fluctuations in axial direction.

Analysis of Azimuthal Thermo-acoustic Modes in Annular Gas Turbine Combustion Chambers

2015 ◽  
Vol 137 (6) ◽  
Author(s):  
Mirko R. Bothien ◽  
Nicolas Noiray ◽  
Bruno Schuermans
Keyword(s):  
Gas Turbine ◽  
Network Model ◽  
Growth Rates ◽  
Linear Growth ◽  
Flame Temperature ◽  
Full Scale ◽  
Linear Growth Rate ◽  
Combustion Chambers ◽  
Engine Operation ◽  
Acoustic Modes

Modern gas turbine combustors operating in lean-premixed mode are prone to thermo-acoustic instabilities. In annular combustion chambers, usually azimuthal acoustic modes are the critical ones interacting with the flame. In case of constructive interference, high amplitude oscillations might result. In this paper, the azimuthal acoustic field of a full-scale engine is investigated in detail. The analyses are based on measurements in a full-scale gas turbine, analytical models to derive the system dynamics, as well as simulations performed with an in-house 3d nonlinear network model. It is shown that the network model is able to reproduce the behavior observed in the engine. Spectra, linear growth rates, as well as the statistics of the system's dynamics can be predicted. A previously introduced algorithm is used to extract linear growth rates from engine and model time domain data. The method's accuracy is confirmed by comparison of the routine's results to analytically determined growth rates from the network model. The network model is also used to derive a burner staging configuration, resulting in the decrease of linear growth rate and thus an increase of engine operation regime; model predictions are verified by full-scale engine measurements. A thorough investigation of the azimuthal modes statistics is performed. Additionally, the network model is used to show that an unfavorable flame temperature distribution with an amplitude of merely 1% of the mean flame temperature can change the azimuthal mode from dominantly rotating to dominantly standing. This is predicted by the network model that only takes into account flame fluctuations in axial direction.

CFD ANALYSIS OF FIRST STAGE NOZZLE COOLING OPTIMIZATION IN POWER STATION GAS TURBINE

2015 ◽  
Vol 76 (5) ◽  
Author(s):  
Hasril Hasini ◽  
Siti Sarah Ain Fadhil ◽  
Mohd Nasharuddin Mohd Jaafar ◽  
Norhazwani Abdul Malek ◽  
Mohd. Haffis Ujir
Keyword(s):  
Gas Turbine ◽  
Transfer Problem ◽  
Maximum Yield ◽  
Safety Margin ◽  
Power Station ◽  
Case Scenario ◽  
Preliminary Calculation ◽  
Worst Case ◽  
Cloud Data ◽  
Computational Fluid Dynamics Analysis

Computational Fluid Dynamics analysis on First Stage Nozzle in full scale multi-stage power station gas turbine has been carried out. The main aim is to investigate the turbine thermal performance when cooling rate decreases at certain level. All calculations were executed using commercial CFD code, ANSYS FLUENT which is able to accurately predict the flow and conjugate heat transfer problem as demonstrated in this investigation. The modelling of gas turbine nozzle is assisted by geometric cloud data obtained from 3D scan. Preliminary calculation shows that at the given worst case scenario for, the maximum thermal stress experienced by the component is within the maximum yield strength of the nozzle material. However, the safety margin between the predicted stress and maximum allowable stress is very small. 

scholarly journals Quantifying acoustic damping using flame chemiluminescence

2016 ◽  
Vol 808 ◽  
pp. 245-257 ◽  
Author(s):  
E. Boujo ◽  
A. Denisov ◽  
B. Schuermans ◽  
N. Noiray
Keyword(s):  
Growth Rate ◽  
Time Series ◽  
Gas Turbines ◽  
Linear Growth ◽  
Dynamic Pressure ◽  
Cost Effective ◽  
Operating Conditions ◽  
Linear Growth Rate ◽  
Acoustic Damping ◽  
Output Only

Thermoacoustic instabilities in gas turbines and aeroengine combustors fall within the category of complex systems. They can be described phenomenologically using nonlinear stochastic differential equations, which constitute the grounds for output-only model-based system identification. It has been shown recently that one can extract the governing parameters of the instabilities, namely the linear growth rate and the nonlinear component of the thermoacoustic feedback, using dynamic pressure time series only. This is highly relevant for practical systems, which cannot be actively controlled due to a lack of cost-effective actuators. The thermoacoustic stability is given by the linear growth rate, which results from the combination of the acoustic damping and the coherent feedback from the flame. In this paper, it is shown that it is possible to quantify the acoustic damping of the system, and thus to separate its contribution to the linear growth rate from the one of the flame. This is achieved by postprocessing in a simple way simultaneously acquired chemiluminescence and acoustic pressure data. It provides an additional approach to further unravel from observed time series the key mechanisms governing the system dynamics. This straightforward method is illustrated here using experimental data from a combustion chamber operated at several linearly stable and unstable operating conditions.

scholarly journals Effect of Radial Wavevector on Collisional Drift Waves in a Toroidal Heliac

1999 ◽  
Vol 52 (1) ◽  
pp. 71 ◽  
Author(s):  
J. L. V. Lewandowski ◽  
R. M. Ellem
Keyword(s):  
Growth Rate ◽  
Electrostatic Potential ◽  
Growth Rates ◽  
Initial Value Problem ◽  
Linear Growth ◽  
Field Model ◽  
Linear Growth Rate ◽  
Drift Waves ◽  
Initial Value ◽  
Magnetic Shear

A 3-field model for collisional drift waves, in the ballooning representation, for a low-pressure stellarator plasma is presented. In particular, the effect of a finite radial mode number (≡ θk) is studied, and the linear growth rates for the fluctuating plasma density, electrostatic potential and electron temperature are computed numerically by solving the 3-field model as an initial-value problem. Numerical results for a 3-field period stellarator with low global magnetic shear are then presented. It is found that, in a system with small global magnetic shear, the case θk = 0 yields the fastest linear growth rate.

Further investigation of 3D dose verification in proton therapy utilizing acoustic signal, wavelet decomposition and machine learning

2021 ◽  
Author(s):  
Songhuan Yao ◽  
Zongsheng Hu ◽  
Qiang Xie ◽  
Yidong Yang ◽  
Hao Peng
Keyword(s):  
Machine Learning ◽  
Proton Therapy ◽  
Acoustic Signal ◽  
Wavelet Decomposition ◽  
Short Term Memory ◽  
Three Dimensions ◽  
Dose Verification ◽  
Case Scenario ◽  
Worst Case ◽  
Dose Distributions

Abstract Online dose verification in proton therapy is a critical task for quality assurance. We further studied the feasibility of using a wavelet-based machine learning framework to accomplishing that goal in three dimensions, built upon our previous work in 1D. The wavelet decomposition was utilized to extract features of acoustic signals and a bidirectional long-short-term memory (Bi-LSTM) recurrent neural network (RNN) was used. The 3D dose distributions of mono-energetic proton beams (multiple beam energies) inside a 3D CT phantom, were generated using Monte-Carlo simulation. The 3D propagation of acoustic signal was modeled using the k-Wave toolbox. Three different beamlets (i.e. acoustic pathways) were tested, one with its own model. The performance was quantitatively evaluated in terms of mean relative error (MRE) of dose distribution and positioning error of Bragg peak (△BP ), for two signal-to-noise ratios (SNRs). Due to the lack of experimental data for the time being, two SNR conditions were modeled (SNR=1 and 5). The model is found to yield good accuracy and noise immunity for all three beamlets. The results exhibit an MRE below 0.6% (without noise) and 1.2% (SNR= 5), and △BP below 1.2 mm (without noise) and 1.3 mm (SNR= 5). For the worst-case scenario (SNR=1), the MRE and △BP are below 2.3% and 1.9 mm, respectively. It is encouraging to find out that our model is able to identify the correlation between acoustic waveforms and dose distributions in 3D heterogeneous tissues, as in the 1D case. The work lays a good foundation for us to advance the study and fully validate the feasibility with experimental results.

Customer Adapted Maintenance Plan (CAMP): A Process for Optimization of Gas Turbine Maintenance

2008 ◽  
Author(s):  
Mathias Wa¨rja ◽  
Pontus Slottner ◽  
Markus Bohlin
Keyword(s):  
Gas Turbine ◽  
Preventive Maintenance ◽  
Gas Turbines ◽  
Measurement Techniques ◽  
Test Methods ◽  
Detailed Knowledge ◽  
Critical Systems ◽  
Case Scenario ◽  
Worst Case ◽  
Maintenance Plan

Maintaining high levels of availability and reliability are essential objectives for many industries, especially those that are subject to high costs due to shutdowns of critical systems, e.g. gas turbines. To utilize these systems as effectively as possible, preventive maintenance must be optimized. Determining what is optimal is, however, a multi-variable task requiring detailed knowledge about the components in the system and their different damage mechanisms. These factors have always affected the condition of the gas turbine and maintenance actions, but only recently has it been possible to estimate and measure them correctly for individual components during operation. In the past, it was necessary to construct maintenance intervals from the most critical component (or components), requiring the highest maintenance frequency. An additional worst-case scenario margin was also necessary, taking into account factors such as possible load variation, differences in environment (affecting e.g. power turbine temperatures) and other sources of uncertainty. These uncertainties together have determined traditional maintenance planning, with maintenance packages each containing a set of maintenance activities for a set of components being predetermined and preplanned. With the new CAMP approach, the maintenance strategy is to reach a Retirement For Cause (RFC) strategy, where components are not replaced until a potential failure has been detected. This requires measurement techniques that can monitor how the gas turbine is operated, prognostics capabilities that foresee maintenance needs, and test methods that can determine the state of a component during maintenance events. One important part of CAMP is therefore a prognostic tool which tells us the condition, and therefore the maintenance needs, of individual components within the gas turbine. To handle this information and efficiently make a preventive maintenance plan, software for gas turbine maintenance optimization has been developed. The software can not only calculate the most efficient point in time for a maintenance action, it can also adjust the maintenance plan to any customer’s specific demands. This paper describes the model, gathering and processing of information, risk assessment performance and the result from an optimization which groups maintenance actions as a result of customer prioritized demands. It also describes the software layout and how it is used.

scholarly journals On the non-axisymmetric fragmentation of rings generated by the Secular Gravitational Instability

2021 ◽  
Author(s):  
Arnaud Pierens
Keyword(s):  
Growth Rate ◽  
Growth Rates ◽  
Linear Growth ◽  
Gravitational Instability ◽  
Dust Particles ◽  
Linear Growth Rate ◽  
Stability Parameters ◽  
Dust Density ◽  
Linear Evolution ◽  
Non Linear

Abstract Ringed structures have been observed in a variety of protoplanetary discs. Among the processes that might be able to generate such features, the Secular Gravitational Instability (SGI) is a possible candidate. It has also been proposed that the SGI might lead to the formation of planetesimals during the non-linear phase of the instability. In this context, we employ two-fluid hydrodynamical simulations with self-gravity to study the non-axisymmetric, non-linear evolution of ringed perturbations that grow under the action of the SGI. We find that the non-linear evolution outcome of the SGI depends mainly on the initial linear growth rate. For SGI growth rates smaller than typically σ ≳ 10−4 − 10−5Ω, dissipation resulting from dust feedback introduces a m = 1 spiral wave in the gas, even for Toomre gas stability parameters Qg > 2 for which non-axisymmetric instabilities appear in a purely gaseous disc. This one-armed spiral subsequently traps dust particles until a dust-to-gas ratio ε ∼ 1 is achieved. For higher linear growth rates, the dust ring is found to undergo gravitational collapse until the bump in the surface density profile becomes strong enough to trigger the formation of dusty vortices through the Rossby Wave Instability (RWI). Enhancements in dust density resulting from this process are found to scale with the linear growth rate, and can be such that the dust density is higher than the Roche density, leading to the formation of bound clumps. Fragmentation of axisymmetric rings produced by the SGI might therefore appear as a possible process for the formation of planetesimals.

On the Effect of Noise Induced Dynamics on Linear Growth Rates of Oscillations in an Electroacoustic Rijke Tube Simulator

2021 ◽  
Author(s):  
Neha Vishnoi ◽  
Pankaj Wahi ◽  
Aditya Saurabh ◽  
Lipika Kabiraj
Keyword(s):  
Gas Turbine ◽  
Turbulent Flows ◽  
Growth Rates ◽  
Noise Intensity ◽  
Linear Growth ◽  
Stochastic Dynamics ◽  
Decay Rates ◽  
System Stability ◽  
Rijke Tube ◽  
The Stability

Abstract Suppressing self-excited thermoacoustic oscillations in combustion chambers is essential for gas turbine system stability. Passive acoustic damping devices such as Helmholtz resonators are commonly employed in modern combustors to address the problem of thermoacoustic instabilities. The estimation of deterministic parameters characterizing flame-acoustic coupling, specifically the stability margins and linear growth/decay rates, is a prerequisite for designing these devices. As gas turbine combustors are typically noisy systems due to the presence of highly turbulent flows and unsteady combustion, it is essential to understand the role of noise and its impact on the estimated system stability. Recently several new results on the stochastic dynamics of thermoacoustic systems and the use of noise-induced dynamics to estimate system stability characteristics have been reported. In the present work, we study the different approaches previously reported on the estimation of linear growth/decay rates from noise-induced dynamics on an electroacoustic Rijke tube (a prototypical thermoacoustic system) simulator. We estimate the growth rates from noisy data obtained from the subthreshold, bistable, and linearly-unstable regions of the observed subcritical Hopf bifurcation and investigate the effect of additive noise intensity. We find that the noise intensity affects the stability boundaries and the estimated growth rates.

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