scholarly journals Impact of the heat release distribution on high-frequency transverse thermoacoustic driving in premixed swirl flames

2016 ◽  
Vol 9 (3) ◽  
pp. 143-154 ◽  
Author(s):  
Michael Hertweck ◽  
Frederik M Berger ◽  
Tobias Hummel ◽  
Thomas Sattelmayer
Keyword(s):  
Heat Release ◽  
Combustion Chamber ◽  
High Frequency ◽  
Transfer Functions ◽  
Three Dimensional ◽  
Elevated Pressure ◽  
Rayleigh Index ◽  
The Stability ◽  
Stability Limits ◽  
The Impact

Self-excited, high-frequency first transversal thermoacoustic instabilities in a cylindrical combustion chamber equipped with a premixed swirl-stabilized flame are investigated. Phase-locked image analysis of the phenomena shows the displacement of the flame and a higher burning rate in the region of elevated pressure. The impact of diffuser angle and fuel composition on the stability limits and the flame position is investigated. The Rayleigh-Index is computed for a three-dimensional domain based on analytical flame transfer functions for experimentally obtained data of OH*-chemiluminescence as measure for the spatial heat release. Two models from different sources are applied, which describe the interaction between flame and acoustic locally. The axial dependence of the amplitude of the transversal mode is computed by a numerical model, which takes the temperature distribution inside the combustion chamber into account. The comparison of the Rayleigh-Index of different operation points shows a correlation with the stability limits for some, but not for all investigated configurations.

High Frequency Thermoacoustic Modulation Mechanisms in Swirl-Stabilized Gas Turbine Combustors: Part One — Experimental Investigation of Local Flame Response

2016 ◽  
Author(s):  
Frederik M. Berger ◽  
Tobias Hummel ◽  
Michael Hertweck ◽  
Jan Kaufmann ◽  
Bruno Schuermans ◽  
...  
Keyword(s):  
Heat Release ◽  
Gas Turbine ◽  
High Frequency ◽  
Transfer Functions ◽  
Temporal Dynamics ◽  
Dynamic Pressure ◽  
Radon Transforms ◽  
Gas Turbine Combustors ◽  
High Modulation ◽  
The Impact

This paper presents the experimental approach for determination and validation of non-compact flame transfer functions of high frequency, transverse combustion instabilities observed in a generic lean premixed gas turbine combustor. The established non-compact transfer functions describe the interaction of the flame’s heat release with the acoustics locally, which is necessary due to the respective length scales being of the same order of magnitude. Spatio-temporal dynamics of the flame are measured by imaging the OH* chemiluminescence signal, phase-locked to the dynamic pressure at the combustor’s front plate. Radon transforms provide a local insight into the flame’s modulated reaction zone. Applied to different burner configurations, the impact of the unsteady heat release distribution on the thermoacoustic driving potential, as well as distinct flame regions that exhibit high modulation intensity are revealed. Utilizing these spatially distributed transfer functions within thermoacoustic analysis tools (addressed in this joint publication’s part two) allows then to predict transverse linear stability of gas turbine combustors.

A Finite Element Method for Three-Dimensional Analysis of Thermo-acoustic Combustion Instability

2010 ◽  
Vol 133 (1) ◽  
Author(s):  
S. M. Camporeale ◽  
B. Fortunato ◽  
G. Campa
Keyword(s):  
Finite Element ◽  
Heat Release ◽  
Combustion Chamber ◽  
Growth Rates ◽  
Acoustic Waves ◽  
Transfer Functions ◽  
Three Dimensional ◽  
Complex Eigenvalue ◽  
Governing Equations ◽  
Acoustic Instabilities

A method for predicting the onset of acoustically driven combustion instabilities in gas turbine combustor is examined. The basic idea is that the governing equations of the acoustic waves can be coupled with a flame heat release model and solved in the frequency domain. The paper shows that a complex eigenvalue problem is obtained that can be solved numerically by implementing the governing equations in a finite element code. This procedure allows one to identify the frequencies at which thermo-acoustic instabilities are expected and the growth rate of the pressure oscillations, at the onset of instability, when the hypothesis of linear behavior of the acoustic waves can be applied. The method can be applied virtually to any three-dimensional geometry, provided the necessary computational resources that are, anyway, much less than those required by computational fluid dynamics methods proposed for analyzing the combustion chamber under instability condition. Furthermore, in comparison with the “lumped” approach that characterizes popular acoustics networks, the proposed method allows one for much more flexibility in defining the geometry of the combustion chamber. The paper shows that different types of heat release laws, for instance, heat release concentrated in a flame sheet, as well as distributed in a larger domain, can be adopted. Moreover, experimentally or numerically determined flame transfer functions, giving the response of heat release to acoustic velocity fluctuations, can be incorporated in the model. To establish proof of concept, the method is validated at the beginning against simple test cases taken from literature. Over the frequency range considered, frequencies and growth rates both of stable and unstable eigenmodes are accurately evaluated. Then the method is applied to a much more complex annular combustor geometry in order to evaluate frequencies and growth rates of the unstable modes and to show how the variation in the parameters of the heat release law can influence the transition to instability.

High-Frequency Thermoacoustic Modulation Mechanisms in Swirl-Stabilized Gas Turbine Combustors—Part I: Experimental Investigation of Local Flame Response

2017 ◽  
Vol 139 (7) ◽  
Author(s):  
Frederik M. Berger ◽  
Tobias Hummel ◽  
Michael Hertweck ◽  
Jan Kaufmann ◽  
Bruno Schuermans ◽  
...  
Keyword(s):  
Heat Release ◽  
Gas Turbine ◽  
High Frequency ◽  
Transfer Functions ◽  
Dynamic Pressure ◽  
Radon Transforms ◽  
Gas Turbine Combustors ◽  
High Modulation ◽  
Order Of Magnitude ◽  
The Impact

This paper presents the experimental approach for determination and validation of noncompact flame transfer functions of high-frequency, transverse combustion instabilities observed in a generic lean premixed gas turbine combustor. The established noncompact transfer functions describe the interaction of the flame's heat release with the acoustics locally, which is necessary due to the respective length scales being of the same order of magnitude. Spatiotemporal dynamics of the flame are measured by imaging the OH⋆ chemiluminescence signal, phase-locked to the dynamic pressure at the combustor's front plate. Radon transforms provide a local insight into the flame's modulated reaction zone. Applied to different burner configurations, the impact of the unsteady heat release distribution on the thermoacoustic driving potential, as well as distinct flame regions that exhibit high modulation intensity, is revealed. Utilizing these spatially distributed transfer functions within thermoacoustic analysis tools (addressed in this joint publication's Part II) allows then to predict transverse linear stability of gas turbine combustors.

Prediction of the Thermoacoustic Combustion Instabilities in Practical Annular Combustors

2014 ◽  
Vol 136 (9) ◽  
Author(s):  
Giovanni Campa ◽  
Sergio Mario Camporeale
Keyword(s):  
Combustion Chamber ◽  
Three Dimensional ◽  
Design Stage ◽  
Combustion Instabilities ◽  
Combustion Chambers ◽  
Stability Maps ◽  
Dimensional Finite Element ◽  
Practical Tool ◽  
The Stability ◽  
Three Dimensional Finite Element

A three-dimensional finite element code is used for the eigenvalue analysis of the thermoacoustic combustion instabilities modeled through the Helmholtz equation. A full annular combustion chamber, equipped with several burners, is examined. Spatial distributions for the heat release intensity and for the time delay are used for the linear flame model. Burners, connecting the plenum and the chamber, are modeled by means of the transfer matrix method. The influence of the parameters characterizing the burners and the flame on the stability levels of each mode of the system is investigated. The obtained results show the influence of the 3D distribution of the flame on the modes. Additionally, the results show what types of modes are most likely to yield humming in an annular combustion chamber. The proposed methodology is intended to be a practical tool for the interpretation of the thermoacoustic phenomenon (in terms of modes, frequencies, and stability maps) both in the design stage and in the check stage of gas turbine combustion chambers.

scholarly journals Forecasting of Surface Currents via Correcting Wind Stress with Assimilation of High-Frequency Radar Data in a Three-Dimensional Model

2016 ◽  
Vol 2016 ◽  
pp. 1-12 ◽  
Author(s):  
Lei Ren ◽  
Stephen Nash ◽  
Michael Hartnett
Keyword(s):  
Data Assimilation ◽  
High Frequency ◽  
Three Dimensional ◽  
Hf Radar ◽  
Surface Velocity ◽  
Shear Stresses ◽  
Surface Currents ◽  
Dimensional Model ◽  
Three Dimensional Model ◽  
The Impact

This paper details work in assessing the capability of a hydrodynamic model to forecast surface currents and in applying data assimilation techniques to improve model forecasts. A three-dimensional model Environment Fluid Dynamics Code (EFDC) was forced with tidal boundary data and onshore wind data, and so forth. Surface current data from a high-frequency (HF) radar system in Galway Bay were used for model intercomparisons and as a source for data assimilation. The impact of bottom roughness was also investigated. Having developed a “good” water circulation model the authors sought to improve its forecasting ability through correcting wind shear stress boundary conditions. The differences in surface velocity components between HF radar measurements and model output were calculated and used to correct surface shear stresses. Moreover, data assimilation cycle lengths were examined to extend the improvements of surface current’s patterns during forecasting period, especially for north-south velocity component. The influence of data assimilation in model forecasting was assessed using a Data Assimilation Skill Score (DASS). Positive magnitude of DASS indicated that both velocity components were considerably improved during forecasting period. Additionally, the improvements of RMSE for vector direction over domain were significant compared with the “free run.”

scholarly journals Thermal functioning of a tropical reservoir assessed through three-dimensional modelling and high-frequency monitoring

RBRH ◽  
2021 ◽  
Vol 26 ◽  
Author(s):  
Denis Furstenau Plec ◽  
Talita Fernanda das Graças Silva ◽  
Brigitte Vinçon-Leite ◽  
Nilo Nascimento
Keyword(s):  
Water Temperature ◽  
High Frequency ◽  
Three Dimensional ◽  
Frequency Measurement ◽  
Three Dimensional Model ◽  
Anthropogenic Pressures ◽  
Tropical Reservoir ◽  
River Temperature ◽  
Lake Morphology ◽  
The Impact

ABSTRACT Urban lakes and reservoirs provide important ecosystem services. However, their water quality is being affected by anthropogenic pressures. The thermal regime is a strong driver of the vertical transport of nutrients, phytoplankton and oxygen. Thermal stratification can modify biogeochemical processes. In this paper, a three-dimensional hydrodynamic model was implemented and validated with high-frequency measurement of water temperature. The simulation results were in agreement with the measurements. For all simulation period, the model performance was evaluated based on hourly values, presenting a maximum RMSE of 0.65 ºC and Relative Error of 2.08%. The results show that high-frequency measurement associated with a three-dimensional model could help to understand and identify the reasons for the changes in the thermal condition of a shallow urban lake. The impact of the stream inflow on the temperature was highlighted, showing that during higher discharge events, when the river temperature is colder than the lake water, it flows into the lake deeper layers. The inflow water sank to the deeper layers where the lake morphology changes. The model showed an impact along the entire lake, showing the importance of monitoring the inflow water temperature. This modelling tool could be further used to study specific patterns of reservoir hydrodynamics.

scholarly journals Stope Stability Assessment and Effect of Horizontal to Vertical Stress Ratio on the Yielding and Relaxation Zones Around Underground Open Stopes Using Empirical and Finite Element Methods

2017 ◽  
Vol 62 (3) ◽  
pp. 653-669 ◽  
Author(s):  
Mohammadali Sepehri ◽  
Derek Apel ◽  
Wei Liu
Keyword(s):  
Finite Element ◽  
Numerical Methods ◽  
Stress Ratio ◽  
Three Dimensional ◽  
Element Model ◽  
Underground Mine ◽  
Graph Method ◽  
The Stability ◽  
Stability Graph ◽  
The Impact

AbstractPredicting the stability of open stopes can be a challenging task for underground mine engineers. For decades, the stability graph method has been used as the first step of open stope design around the world. However, there are some shortcomings with this method. For instance, the stability graph method does not account for the relaxation zones around the stopes. Another limitation of the stability graph is that this method cannot to be used to evaluate the stability of the stopes with high walls made of backfill materials. However, there are several analytical and numerical methods that can be used to overcome these limitations. In this study, both empirical and numerical methods have been used to assess the stability of an open stope located between mine levels N9225 and N9250 at Diavik diamond underground mine. It was shown that the numerical methods can be used as complementary methods along with other analytical and empirical methods to assess the stability of open stopes. A three dimensional elastoplastic finite element model was constructed using Abaqus software. In this paper a sensitivity analysis was performed to investigate the impact of the stress ratio “k” on the extent of the yielding and relaxation zones around the hangingwall and footwall of the understudy stope.

Influence of plasma-chemical products on process stability in a low-emission gas turbine combustion chamber

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Serhiy Serbin ◽  
Artem Kozlovskyi ◽  
Kateryna Burunsuz
Keyword(s):  
Combustion Chamber ◽  
Gas Turbine ◽  
Fuel Combustion ◽  
Gaseous Fuel ◽  
Plasma Chemical ◽  
Flame Tube ◽  
Low Emission ◽  
Gas Turbine Combustion ◽  
The Stability ◽  
The Impact

Abstract The article describes the stability of gaseous fuel combustion in gas turbine low-emission combustion chambers with the plasma-chemical assistance. The mathematical model of unsteady processes in a low-emission combustion chamber with a plasma-chemical stabilizer that takes into consideration the impact of low-temperature plasma on aerodynamics flow in a combustion chamber and the characteristics of heat release is developed. A methodology of a numerical experiment concerning the stability of gaseous fuel combustion in a combustion chamber with plasma assistance using computational fluid dynamics, which enhances the efficiency of designing and adjustment, is proposed. Practical recommendations for improvement of stability of a gas turbine combustion chamber with partially premixed lean fuel–air mixtures, working on gaseous fuels, are developed. They allow to reduce pressure fluctuations inside the flame tube by 10–35%, to decrease spectral power of static pressure in the flame tube in 1.5–2.0 times, to reduce nitrogen oxide emission up to 33.6 ppm in the exit section while retaining a carbon monoxide emission level, that corresponds modern international ecological standards.

A Unified Transfer Function (UTF) Approach for the Modeling and Stability Analysis of Long Slender Bars in 3-D Turning Operations

1993 ◽  
Vol 115 (2) ◽  
pp. 193-204 ◽  
Author(s):  
I. N. Tansel
Keyword(s):  
Stability Analysis ◽  
Transfer Function ◽  
Transfer Functions ◽  
Experimental Studies ◽  
Three Dimensional ◽  
Tool Geometry ◽  
Turning Operations ◽  
Chip Area ◽  
The Stability ◽  
Unique Relationship

A new approach is introduced to model 3-D turning operations that are used for the stability analysis of long slender bars. This approach utilizes the unique relationship between externally created feed direction tool displacements (input) and the resultant thrust direction workpiece vibrations (output) to estimate stability limits in three-dimensional turning operations from the data of a single dynamic cutting test. In this paper, this unique relationship is referred to as the “Unified Transfer Function ” (UTF) and its expressions are derived from conventional cutting and structural dynamics transfer functions. For the stability analysis, the uncut chip area variations of oblique cutting are represented by a linear model having different coefficients at different depths of cuts. These coefficients are found by using a tool geometry simulation program. An iterative procedure is developed for the stability analysis. The proposed approach considers in-process structural and cutting dynamics and can be automatically implemented without any input from the operator for the traverse turning of a long slender bar. Experimental studies have validated the proposed modeling and stability analysis techniques. The UTFs can also be used to monitor machine tool structure, tool wear, and the machinability of the material.

Analysis of a diesel engine fueled with ternary fuel blends and alumina nano-additives at various combustion chamber geometries

2020 ◽  
pp. 1-12 ◽  
Author(s):  
George Antony Casmir Jayaseelan ◽  
Anderson Arul Gnana Dhas ◽  
Harish Venu ◽  
Jayaprabakar Jayaraman ◽  
Prabhu Appavu
Keyword(s):  
Heat Release ◽  
Combustion Chamber ◽  
Heat Release Rate ◽  
Release Rate ◽  
Combustion Zone ◽  
High Performance ◽  
Specific Energy Consumption ◽  
Fuel Mixture ◽  
Nano Additives ◽  
The Impact

The present study investigates the impact of various combustion chamber geometries in a direct injection engine fueled with diesel–biodiesel–ethanol blends mixed with alumina nano-additives, named as high-performance fuel (HPF). The HPF was subjected to various combustion bowl geometries including standard hemispherical chamber geometry (SG), shallow depth reentrant bowl geometry (CG1), toroidal reentrant chamber geometry (CG2), and toroidal chamber geometry (CG3). Performance results reveal that in comparison with the SG-HPF arrangement, brake thermal efficiency increased by 11.51% and brake-specific energy consumption decreased by 10.37% when using the CG2-HPF arrangement. For emmisions, CG2-HPF reduced carbon monoxide, hydrocarbon, and smoke emissions by 33.53%, 18.35%, and 14.37%, respectively, in comparison with SG-HPF. Regarding combustion, CG2-HPF resulted in a high heat release rate owing to the reentrant chamber profile of CG2 which improves the air–fuel mixture rate, atomization, and evaporation rate, resulting in more efficient combustion, increased cylinder pressure, and increased heat release rate. Thanks to the geometry of the reentrant profile, the turbulent kinetic energy of the fuel mixture is maintained and returned to the combustion zone. Thus, the stagnation of rich mixtures within the combustion zone tend to decrease. Overall, the CG2 geometry was found to be the optimum geometry profile for HPF, based on improved performance and combustion characteristics, as well as reduced exhaust emissions.

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