Passive Control of Limit Cycle Oscillations in a Thermoacoustic System Using Asymmetry

2008 ◽  
Vol 75 (1) ◽  
Author(s):  
Bryan Eisenhower ◽  
Gregory Hagen ◽  
Andrzej Banaszuk ◽  
Igor Mezić
Keyword(s):  
Limit Cycle ◽  
Passive Control ◽  
Combustion Process ◽  
System Response ◽  
Nonlinear Feedback ◽  
Gas Turbine Combustor ◽  
Temporal Averaging ◽  
Parameter Values ◽  
Physical Phenomena ◽  
Heat Released

In this paper we investigate oscillations of a dynamical system containing passive dynamics driven by a positive feedback and how spatial characteristics (i.e., symmetry) affect the amplitude and stability of its nominal limit cycling response. The physical motivation of this problem is thermoacoustic dynamics in a gas turbine combustor. The spatial domain is periodic (passive annular acoustics) which are driven by heat released from a combustion process, and with sufficient driving through this nonlinear feedback a limit cycle is produced which is exhibited by a traveling acoustic wave around this annulus. We show that this response can be controlled passively by spatial perturbation in the symmetry of acoustic parameters. We find the critical parameter values that affect this oscillation, study the bifurcation properties, and subsequently use harmonic balance and temporal averaging to characterize periodic solutions and their stability. In all of these cases, we carry a parameter associated with the spatial symmetry of the acoustics and investigate how this symmetry affects the system response. The contribution of this paper is a unique analysis of a particular physical phenomena, as well as illustrating the equivalence of different nonlinear analysis tools for this analysis.

Suppression of Combustion Noise in Gas Turbine Combustors

2015 ◽  
Author(s):  
Srihari Dinesh Kumar Juvva ◽  
Sathesh Mariappan ◽  
Abhijit Kushari
Keyword(s):  
Gas Turbine ◽  
Pressure Transducer ◽  
Passive Control ◽  
Broad Band ◽  
Combustion Process ◽  
Combustion Noise ◽  
Acoustic Oscillations ◽  
Gas Turbine Combustor ◽  
Direct Combustion ◽  
Aviation Turbine Fuel

This study deals with the investigations on the sources and the control of combustion noise, in an atmospheric gas turbine combustor. Combustion noise encountered here is also termed as hooting, as it occurs within a limited bandwidth of frequencies ranging from 300–450 Hz. Combustion noise is usually classified as direct and in-direct combustion noise. The present study emphases on the direct combustion noise which occurs when a volume of gas expands at constant pressure, as soon as it is heated by combustion; this results in a sound wave which propagates outside the boundary of the flame. At certain conditions, if the unsteady heat release rate drives the acoustic oscillations, satisfying Rayleigh criterion, pressure oscillations grow leading to discrete tonal sound and this phenomena is termed as combustion instability. Experiments are conducted in a liquid fuelled swirl stabilized atmospheric gas turbine combustor, whose aspect ratio is 2.5, combustion intensity varies from 25MW/m3 atm to 50MW/m3 atm. Air is passed through various stages: primary, secondary, quenching and atomizing air. Aviation turbine fuel is injected through an air-blast atomizer. An unsteady pressure transducer is located at the primary zone to measure the acoustic oscillations. The frequency of sound generated during the combustion process is compared with a microphone located at 1.25 m away from the combustor at an angle of 45° from the axis of the combustor. The main objective of this paper is to investigate the cause of hooting and the passive control techniques in order to reduce it. This is achieved by two ways, systematically by two ways, i) reducing the quenching air methodologically reducing the quenching air and ii) varying the air to liquid (fuel) ratio (ALR). By imparting these methods the sound pressure level inside the combustor is reduced from 143dB to 128dB. Since, combustion noise occurs in a broad-band of frequencies, the unsteady data obtained with the pressure transducer are analyzed using octave bands, where it shows linear decrement of energy present in-between the two frequencies. In order to perform parametric study, two swirlers of swirl numbers.0.77 and 0.86 are used. Established by the physics of Helmholtz oscillator, the combustor hooting is dictated, by which the sound produced by the combustor is explained.

scholarly journals The Synergy of Two Biofuel Additives on Combustion Process to Simultaneously Reduce NOx and PM Emissions

Energies ◽  
2021 ◽  
Vol 14 (10) ◽  
pp. 2784
Author(s):  
Jerzy Cisek ◽  
Szymon Lesniak ◽  
Winicjusz Stanik ◽  
Włodzimierz Przybylski
Keyword(s):  
Heat Release ◽  
Combustion Rate ◽  
Combustion Process ◽  
The Other ◽  
Fuel Additive ◽  
Exhaust Gas ◽  
Synergy Effect ◽  
Engine Exhaust ◽  
Other Hand ◽  
Heat Released

The article presents the results of research on the influence of two fuel additives that selectively affect the combustion process in a diesel engine cylinder. The addition of NitrON® reduces the concentration of nitrogen oxides (NOx), due to a reduction in the kinetic combustion rate, at the cost of a slight increase in the concentration of particulate matter (PM) in the engine exhaust gas. The Reduxco® additive reduces PM emissions by increasing the diffusion combustion rate, while slightly increasing the NOx concentration in the engine exhaust gas. Research conducted by the authors confirmed that the simultaneous use of both of these additives in the fuel not only reduced both NOx and PM emissions in the exhaust gas but additionally the reduction of NOx and PM emissions was greater than the sum of the effects of these additives—the synergy effect. Findings indicated that the waveforms of the heat release rate (dQ/dα) responsible for the emission of NOx and PM in the exhaust gas differed for the four tested fuels in relation to the maximum value (selectively and independently in the kinetic and diffusion stage), and they were also phase shifted. Due to this, the heat release process Q(α) was characterized by a lower amount of heat released in the kinetic phase compared to fuel with NitrON® only and a greater amount of heat released in the diffusion phase compared to fuel with Reduxco® alone, which explained the lowest NOx and PM emissions in the exhaust gas at that time. For example for the NOx concentration in the engine exhaust: the Nitrocet® fuel additive (in the used amount of 1500 ppm) reduces the NOx concentration in the exhaust gas by 18% compared to the base fuel. The addition of a Reduxco® catalyst to the fuel (1500 ppm) unfortunately increases the NOx concentration by up to 20%. On the other hand, the combustion of the complete tested fuel, containing both additives simultaneously, is characterized, thanks to the synergy effect, by the lowest NOx concentration (reduction by 22% in relation to the base). For example for PM emissions: the Nitrocet® fuel additive does not significantly affect the PM emissions in the engine exhaust (up to a few per cent compared to the base fuel). The addition of a Reduxco® catalyst to the fuel greatly reduces PM emissions in the engine exhaust, up to 35% compared to the base fuel. On the other hand, the combustion of the complete tested fuel containing both additives simultaneously is characterized by the synergy effect with the lowest PM emission (reduction of 39% compared to the base fuel).

The Role of the Recirculating Gases at the Mild Combustion Regime Formation

2007 ◽  
Author(s):  
Y. Levy ◽  
V. Sherbaum ◽  
V. Erenburg
Keyword(s):  
Gas Turbine ◽  
Ignition Delay ◽  
Ignition Delay Time ◽  
Combustion Process ◽  
Combustion Regime ◽  
Reaction Products ◽  
Gas Turbine Combustor ◽  
Mild Combustion ◽  
Recirculation Rate ◽  
Co Emission

The present work is concerned with the thermodynamic and chemical kinetics of gas turbine combustor operating in the Moderate or Intense Low-oxygen Dilution (MILD) combustion regime. The objective of the present study is to evaluate analytically the effect of the recirculation rate of combustion products within the FLOXCOM gas turbine combustor on a number of combustion parameters, mainly on the ignition delay time, NOx and CO emission, minimum ignition temperature, rate of pollutant formation and the dilution rate. The study also refers to the mechanism of influence of the recirculation rate on these values. Combustion pressure and inlet air temperature are used as parameters. The gas turbine is fueled with methane. The analysis is mainly based on CHEMKIN simulations where the calculation scheme of the combustion process in the combustor is modeled by a combination of plug reactors and mixers. Due to the unique characteristics of gas turbines, inlet air temperature is directly linked to combustion pressure while assuming conventional adiabatic compression efficiencies. It is shown that free radicals, which are part of the reaction products and exists for only a short period of time within the recirculated gases, decrease ignition delay time. The importance of shortening the ignition delay is further highlighted because of the adverse effect oxygen dilution has on this parameter (dilution of the reactants by the reaction products). It was found that there is an optimal recirculation rate, which corresponds to maximum heat density. In addition, results indicate that CO emission values rise with the recirculation rate, however the NOX values are more complicated. NOX depends on recirculation rate when flame temperatures are kept held constant. The NOX emission increases and the CO emission decreases with compressor pressure ratio. The CO concentration that is evaluated in the combustion process is further reduced during last dilution stage. Finally, basic rules for design optimization of the combustor are drafted. These are based on conventional one-dimensional fluid and thermodynamic relations and on the CHEMKIN simulations.

The Effect of Structural Parameters on Response Characteristics of Aeroelastic System in the Presence of Dynamic Stall

2021 ◽  
Author(s):  
Zhan Qiu ◽  
Fuxin Wang
Keyword(s):  
Limit Cycle ◽  
Structural Parameters ◽  
Dynamic Pressure ◽  
Angle Of Attack ◽  
Dynamic Stall ◽  
System Response ◽  
Structural Stiffness ◽  
Aeroelastic System ◽  
Equilibrium Angle ◽  
Minimum Angle

Abstract The effect of structural paramters on the response and aerodynamic stiffness characteristics of the free aeroelastic system under the influence of dynamic stall is investigated adopting CFD (Computational Fluid Dynamics) method. The equilibrium angle of the spring and the structural stiffness are taken as parameters of interest. Systems with small equilibrium angles enter the symmetric limit-cycle state more quickly after a Hopf bifurcation and experience dynamic stall in both directions, rather than slowly decreasing in minimum angle of attack and remaining in the asymmetric limit-cycle state before dynamic stall in the opposite direction, as is the case with systems with large spring equilibrium angles. Thus, aerodynamic stiffness of system with large equilibrium angles can be more significantly influenced by the change in aerodynamic moment characteristics at the minimum angle of attack. Furthermore, by increasing the initial angular velocity, we find that the system response all becomes symmetric limit cycle and therefore the aerodynamic stiffness appears to have a monotonically increasing characteristic. As to the effect of structural stiffness, it is found that the limit cycle amplitude first increases with structural stiffness after bifurcation, then the amplitude is unchanged with varying structural stiffness at higher Mach number. Energy maps show that the parametric distribution of the energy transfer contributes to this phenomenon. Moreover, when entering the symmetric limit cycle state, the structural stiffness no longer has a significant effect on the aerodynamic stiffness of the system, as the increase in the aerodynamic stiffness is determined solely by the increase in dynamic pressure without the effect of changes in moment characteristics.

scholarly journals Rendering a subcritical Hopf bifurcation supercritical

1996 ◽  
Vol 317 ◽  
pp. 91-109 ◽  
Author(s):  
Po Ki Yuen ◽  
Haim H. Bau
Keyword(s):  
Hopf Bifurcation ◽  
Limit Cycle ◽  
Thermal Convection ◽  
Control Strategy ◽  
Chaotic Motion ◽  
Feedback Controller ◽  
Nonlinear Feedback ◽  
Naturally Occurring ◽  
Subcritical Hopf Bifurcation ◽  
Stable Periodic

It is demonstrated experimentally and theoretically that through the use of a nonlinear feedback controller, one can render a subcritical Hopf bifurcation supercritical and thus dramatically modify the nature of the flow in a thermal convection loop heated from below and cooled from above. In particular, we show that the controller can replace the naturally occurring chaotic motion with a stable, periodic limit cycle. The control strategy consists of sensing the deviation of fluid temperatures from desired values at a number of locations inside the loop and then altering the wall heating to counteract such deviations.

Stability, Bifurcation and Jumping Phenomenon in a 2-D Model of Supersonic Lifting Surfaces

2005 ◽  
Author(s):  
Pei Yu ◽  
Zhen Chen ◽  
Liviu Librescu ◽  
Piergiovanni Marzocca
Keyword(s):  
Nonlinear Feedback ◽  
Feedback Controls ◽  
Normal Form Theory ◽  
Center Manifold Reduction ◽  
Form Theory ◽  
Lifting Surfaces ◽  
The Stability ◽  
Parameter Values ◽  
Manifold Reduction ◽  
D Model

This paper is concerned with the linear/nonlinear aeroelastic control of 2-D supersonic lifting surfaces. Its goal is to provide the feedback control mechanism enabling one to enlarge the flight envelope by increasing the flutter speed, and also to control the character, benign/catastrophic of the flutter instability boundary. Structural and aerodynamic nonlinearities are included in the aeroelastic governing equations, and linear and nonlinear feedback controls in both plunging and pitching are employed in conjunction with proportional velocity feedback controls. The attention of the paper is focused on multiple Hopf bifurcations. In particular, the jumping phenomenon found in our previous work will be further investigated to reveal the physical implications. It is found that such a jumping occurs when the system has multiple families of limit cycles bifurcating from a same set of parameter values with multiple solutions for frequencies. The case investigated in this paper is restricted to zero structure damping. Center manifold reduction and normal form theory are applied to consider the stability of post-flutter solutions and the associated jumping phenomenon. Numerical simulations are presented to show the implications of time delay in the considered controls.

scholarly journals Cardiovascular Modeling With Adapted Parametric Inference

2018 ◽  
Vol 62 ◽  
pp. 91-107 ◽  
Author(s):  
Didier Lucor ◽  
Olivier P. Le Maître
Keyword(s):  
Approximation Error ◽  
Surrogate Models ◽  
Patient Specific ◽  
System Response ◽  
Cardiovascular Parameter ◽  
Monte Carlo Algorithms ◽  
Statistical Framework ◽  
Posterior Sampling ◽  
Powerful Approach ◽  
Parameter Values

Computational modeling of the cardiovascular system, promoted by the advance of fluid-structure interaction numerical methods, has made great progress towards the development of patient-specific numerical aids to diagnosis, risk prediction, intervention and clinical treatment. Nevertheless, the reliability of these models is inevitably impacted by rough modeling assumptions. A strong in-tegration of patient-specific data into numerical modeling is therefore needed in order to improve the accuracy of the predictions through the calibration of important physiological parameters. The Bayesian statistical framework to inverse problems is a powerful approach that relies on posterior sampling techniques, such as Markov chain Monte Carlo algorithms. The generation of samples re-quires many evaluations of the cardiovascular parameter-to-observable model. In practice, the use of a full cardiovascular numerical model is prohibitively expensive and a computational strategy based on approximations of the system response, or surrogate models, is needed to perform the data as-similation. As the support of the parameters distribution typically concentrates on a small fraction of the initial prior distribution, a worthy improvement consists in gradually adapting the surrogate model to minimize the approximation error for parameter values corresponding to high posterior den-sity. We introduce a novel numerical pathway to construct a series of polynomial surrogate models, by regression, using samples drawn from a sequence of distributions likely to converge to the posterior distribution. The approach yields substantial gains in efficiency and accuracy over direct prior-based surrogate models, as demonstrated via application to pulse wave velocities identification in a human lower limb arterial network.

Effect of Ti Contents on the Microstructure and Mechanical Properties of Ni˗Al˗Ti System

2020 ◽  
Vol 991 ◽  
pp. 24-29
Author(s):  
Dhimas Wicaksono ◽  
Xiao Meng Zhu ◽  
Mohammad Sukri Mustapa ◽  
Sulis Yulianto ◽  
Ahmad Yunus Nasution ◽  
...  
Keyword(s):  
Vickers Microhardness ◽  
Combustion Process ◽  
Intermetallic Phases ◽  
External Heat ◽  
Temperature Synthesis ◽  
Mixed Powder ◽  
External Heat Source ◽  
High Temperature Synthesis ◽  
Ti Content ◽  
Heat Released

In this work, a ternary system prepared by Ni-Al-Ti mixed powder was synthesized using self-propagation high-temperature synthesis (SHS) process. The weight of the reactant was varied using 3%, 10%, 20% and 30% of the Ti content. The mixtures were compressed in a steel die to form compacted pellets, and subsequently ignited using an external heat source to initiate the combustion process. The synthesized products were characterized using SEM, EDS, and XRD, whereas the mechanical property of the product was measured using a Vickers microhardness test. The identification of the formed phase indicates that Ni-Al, Ti-Al and Ti-Ni systems were formed during the reaction. An increase of Ti content from 3% to 10% improves the density of the synthesized product. Further increase of Ti content to 20% results in the generation of cracks. The addition of Ti with 30% leads to the formation of a porous product. The heat released by the SHS process due to the formation of several intermetallic phases was responsible for the formation of defect products. The highest hardness of the product was achieved in the product prepared by 20% Ti content. However, the higher Ti content than 20% results in hardness reduction. This work shows that the content of 10% of Ti produced a dense and hard product.

Preliminary CFD Investigation of Syngas Combustion at Different Operating Pressures

2015 ◽  
Vol 786 ◽  
pp. 215-219
Author(s):  
Norhaslina Mat Zian ◽  
Hasril Hasini ◽  
Nur Irmawati Om
Keyword(s):  
Temperature Distribution ◽  
Thermal Power ◽  
Combustion Process ◽  
Pressure Variation ◽  
Operating Pressure ◽  
Gas Turbine Combustor ◽  
Average Temperature ◽  
Conventional Combustion ◽  
Synthetic Gas ◽  
Syngas Combustion

Study on the flow and combustion behavior inside gas turbine combustor used in thermal power plant is described in this paper. The combustion process takes place using synthetic gas and emphasis is given to the effect of pressure variation on flame profile, temperature distribution and emissions as compared to the conventional combustion using methane. The operating pressure of the can-type combustor varies in the range of 1-10 atm. while the syngas composition is assumed to have fixed values of 10% CH4, 55% CO, 30% H2 and 5% N2. Preliminary result shows that the flow inside the can-combustor is highly swirling which indicates good mixing of fuel and air prior to the entrance of the mixture to the main combustion zone. The temperature distribution at combustor mid plane show identical pattern for pressure range between 1-10 atm for both maximum and average temperature magnitude.

Comparison of Numerical and Experimental Results of a Premixed DLE Gas Turbine Combustor

2001 ◽  
Author(s):  
Ruud L. G. M. Eggels ◽  
Christopher T. Brown
Keyword(s):  
Reaction Mechanism ◽  
Gas Turbine ◽  
Combustion Process ◽  
Combustion Efficiency ◽  
Gas Turbine Combustor ◽  
Cfd Modelling ◽  
Recirculation Length ◽  
Global Reaction ◽  
Presumed Pdf ◽  
Pdf Model

A numerical and experimental study on a premixed DLE gas turbine combustor has been performed. Experiments and CFD modelling have been carried out at isothermal and combusting conditions. The measurements were obtained at ERC using two component Laser Doppler Velocimetry. To be able to access the inner part of the combustor, the liners of the combustion chamber were outfitted with quartz windows. Temperature measurements were obtained at a few planes using a thermocouple. Modelling of the combustor has been performed using an in-house CFD code. The combustion process has been modelled using a global reaction mechanism and a Flame Generated Manifold reaction mechanism in combination with a presumed PDF model to incorporate the effect of turbulent fluctuations. The Flame Generated Manifold method uses a flame library, which has been generated by performing a number of laminar one-dimensional flame calculations at representative conditions. Comparing the numerical and experimental quite some differences are observed. The CFD model is able to predict the main features of the flow and combustion process, but does not predict the recirculation length accurately. Both combustion models, however, are able to predict the low combustion efficiency measured at the 1atm test condition.

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