Modelling of Circumferential Modal Coupling Due to Helmholtz Resonators

2003 ◽  
Author(s):  
Simon R. Stow ◽  
Ann P. Dowling
Keyword(s):  
Acoustic Waves ◽  
Gas Turbines ◽  
Helmholtz Resonator ◽  
Operating Conditions ◽  
Acoustic Energy ◽  
Radial Dependence ◽  
Helmholtz Resonators ◽  
Annular Duct ◽  
Linear Waves ◽  
Modal Coupling

Lean premixed prevaporised (LPP) combustion can reduce NOx emissions from gas turbines, but often leads to combustion instability. Acoustic waves produce fluctuations in heat release, for instance by perturbing the fuel-air ratio or flame shape. These heat fluctuations will in turn generate more acoustic waves and in some situations self-sustained oscillations can result. A linear model for thermoacoustic oscillations in LPP combustors is described. A thin annular geometry is assumed and so circumferential modes are included but radial dependence is ignored. The formulation is in terms of a network of modules such as straight ducts and area changes. At certain operating conditions, the flow is predicted to be unstable, with linear waves growing in amplitude. Helmholtz resonators can be used to absorb acoustic energy and, when carefully designed and installed at appropriate locations, can stabilise the flow. Helmholtz resonators are included in the model. Connecting a Helmholtz resonator to an annular duct destroys the axisymmetry of the geometry. This results in coupling of the circumferential modes which must be calculated. The model is used to investigate the best arrangement of resonators around the circumference of an annular duct to achieve maximum damping of a circumferential oscillation.

Acoustic Resonances of an Industrial Gas Turbine Combustion System

2000 ◽  
Vol 123 (4) ◽  
pp. 766-773 ◽  
Author(s):  
S. Hubbard ◽  
A. P. Dowling
Keyword(s):  
Gas Turbine ◽  
Acoustic Waves ◽  
Low Frequency ◽  
Helmholtz Resonator ◽  
Nonlinear Effects ◽  
Operating Conditions ◽  
Resonant Frequencies ◽  
Bulk Mode ◽  
Acoustic Resonances ◽  
Industrial Gas Turbine

A theory is developed to describe low-frequency acoustic waves in the complicated diffuser/combustor geometry of a typical industrial gas turbine. This is applied to the RB211-DLE geometry to give predictions for the frequencies of the acoustic resonances at a range of operating conditions. The main resonant frequencies are to be found around 605 Hz (associated with the plenum) and around 461 Hz and 823 Hz (associated with the combustion chamber), as well as one at around 22 Hz (a bulk mode associated with the system as a whole). The stabilizing effects of a Helmholtz resonator, which models damping through nonlinear effects, are included, together with effects of coupled pressure waves in the fuel supply system.

Acoustic-Structure Interaction in an Adaptive Helmholtz Resonator by Compliance and Constraint

2019 ◽  
Vol 142 (2) ◽  
Author(s):  
Shichao Cui ◽  
Ryan L. Harne
Keyword(s):  
Flexible Structures ◽  
Helmholtz Resonator ◽  
Acoustic Resonator ◽  
Acoustic Energy ◽  
Coupled Resonators ◽  
Acoustic Structure ◽  
Structure Interaction ◽  
Helmholtz Resonators ◽  
Rigid Walls ◽  
Flexible Member

Abstract The acoustic energy attenuation capabilities of traditional Helmholtz resonators are enhanced by various methods, including by coupled resonators, absorbing materials, or replacement of rigid walls with flexible structures. Drawing from these concepts to envision a new platform of adaptive Helmholtz resonator, this research studies an adaptive acoustic resonator with an internal compliant structural member. The interaction between the structure and acoustic domain is controlled by compression constraint. By applying uniaxial compression to the resonator, the flexible member may be buckled, which drastically tailors the acoustic-structure interaction mechanisms in the overall system. A phenomenological analytical model is formulated and experimentally validated to scrutinize these characteristics. It is found that the compression constraint may enhance damping capabilities of the resonator by adapting the acoustic-structure interaction between the resonator and the enclosure. The area ratio of the flexible member to the resonator opening and the ratio of the fundamental natural frequency of the flexible member to that of the enclosure are discovered to have a significant influence on the system behavior. These results reveal new avenues for acoustic resonator concepts exploiting compliant internal structures to tailor acoustic energy attenuation properties.

Numerical Simulation of the Acoustic Pressure Field in an Annular Combustion Chamber With Helmholtz Resonators

2004 ◽  
Author(s):  
S. M. Camporeale ◽  
A. Forte ◽  
B. Fortunato ◽  
M. Mastrovito ◽  
A. Ferrante
Keyword(s):  
Combustion Chamber ◽  
Gas Turbines ◽  
Acoustic Pressure ◽  
Pressure Fluctuations ◽  
Low Frequency ◽  
Helmholtz Resonator ◽  
Acoustic Frequency ◽  
Helmholtz Resonators ◽  
Lean Premixed Flames ◽  
Lower Magnitude

In modern gas turbines in which lean premixed flames are used to obtain low NOx emissions, large pressure oscillations may arise inside the combustor due to thermoacoustic combustion instability at frequencies corresponding to the natural acoustic frequency of the system. Such pressure fluctuations, that may cause structural damages, need to be damped in order to avoid a reduction of the operational range of the gas turbine. In this work Helmholtz resonators connected to the external envelope of the combustion chamber are examined as passive systems for damping the low frequency acoustic pressure in the case of an annular combustor. The acoustical behavior of the combustor has been first investigated by means of the Finite Element method, obtaining its acoustic eigenmodes and eigenfrequencies in order to tune the Helmholtz resonators on the frequency to be damped. In order to characterize the resonator, preliminary tests have been carried out on a simplified system composed of a Helmholtz resonator applied at the end of an impedance tube. Then the eigenmodes of the system obtained by connecting one or more resonators to the annular chamber and the damping effects obtained by varying the geometry, the number and the position of the resonators are analyzed. It appears that the peak of acoustic pressure characterizing the combustion chamber splits into two peaks of lower magnitude when the Helmholtz resonators are applied and the peak frequencies are correlated to the overall volume of resonant cavities, whilst lower effects are obtained by varying the position and the number of resonator units.

Thermoacoustic Oscillations in an Annular Combustor

2001 ◽  
Author(s):  
Simon R. Stow ◽  
Ann P. Dowling
Keyword(s):  
Heat Release ◽  
Acoustic Waves ◽  
Gas Turbines ◽  
Radial Dependence ◽  
Sustained Oscillations ◽  
Resonant Modes ◽  
Annular Combustor ◽  
Propagation Matrix ◽  
Flame Shape ◽  
Thermoacoustic Oscillations

Lean premixed prevaporised (LPP) combustion can reduce NOx emissions from gas turbines, but often leads to combustion instability. Acoustic waves produce fluctuations in heat release, for instance by perturbing the fuel–air ratio or flame shape. These heat fluctuations will in turn generate more acoustic waves and in some situations self-sustained oscillations can result. A linear model for thermoacoustic oscillations in LPP combustors is described. A thin annular combustor is assumed and so circumferential modes are included but radial dependence is ignored. The geometry consists of straight ducts joined by short regions of area change. Perturbations to the flow can be thought of as a combination of acoustic, entropy and vorticity waves. The development of these waves along the straight ducts is found using a propagation matrix approach. At the entrance to the combustion chamber, a flame model is used in which the unsteady heat release is related to fluctuations in fuel–air ratio. Various possible inlet and outlet conditions are described. The model is then applied to a simplified example based on a sector rig. The resonant modes are found numerically and compared with the frequencies that occurred in experiments.

scholarly journals Numerical studies of transmission loss performances of asymmetric Helmholtz resonators in the presence of a grazing flow

2018 ◽  
Vol 38 (2) ◽  
pp. 244-254 ◽  
Author(s):  
Zhengli Lu ◽  
Weichen Pan ◽  
Yiheng Guan
Keyword(s):  
Mach Number ◽  
Gas Turbines ◽  
Stokes Equations ◽  
Transmission Loss ◽  
Helmholtz Resonator ◽  
Transmission Losses ◽  
Resonant Frequencies ◽  
Helmholtz Resonators ◽  
Grazing Flow ◽  
Maximum Transmission

As a typical noise-attenuating device, Helmholtz resonators are widely implemented in aero-engines and gas turbines to decrease the transmission of acoustic noise. However, an asymmetric Helmholtz resonator could be designed and implemented due to the limited space available in the engines. To examine and optimize the noise-attenuating performances of the asymmetric resonator, comparison studies are performed. For this, a two-dimensional frequency-domain model of a cylindrical duct with a grazing flow is developed. An asymmetric Helmholtz resonator is attached as a side branch. The model containing the linearized Navier–Stokes equations is validated first by comparing the predicted results with the experimental ones available in the literature. Further validation is conducted by comparing the results of an asymmetric resonator with the analytical ones available in the literature. The effects of (1) neck offset distance from the center of the resonator cavity denoted by [Formula: see text] and (2) the grazing flow Mach number [Formula: see text] are evaluated. It is shown that as the grazing flow Mach number is increased, the resonant frequencies and the maximum transmission losses are dramatically varied for a given [Formula: see text]. As [Formula: see text] is increased from 0 to 0.5 and [Formula: see text], the resonant frequencies and the maximum transmission losses are increased. However, when [Formula: see text] is lower than 0.07, i.e. [Formula: see text], the transmission loss performances are almost unchanged with [Formula: see text] increased. The optimum design of the asymmetric resonator is shown to give rise to the resonant frequency being shifted by 10% and 2–5 dB more transmission loss at higher Mach number. Finally, visualization of vortex shedding formed at the neck of the asymmetric resonator confirms that acoustical energy is transformed into kinetic energy and absorbed by the surrounding air. This study opens up a numerical design approach to optimize an asymmetric resonator.

A Novel Damping Device for Broadband Attenuation of Low-Frequency Combustion Pulsations in Gas Turbines

2012 ◽  
Author(s):  
Mirko R. Bothien ◽  
Nicolas Noiray ◽  
Bruno Schuermans
Keyword(s):  
Gas Turbines ◽  
Low Frequency ◽  
Helmholtz Resonator ◽  
Operating Regime ◽  
Operating Conditions ◽  
Pulsation Frequency ◽  
Dimensional Parameter ◽  
Low Frequencies ◽  
Resonator Design ◽  
Test Engine

Damping of thermoacoustically induced pressure pulsations in combustion chambers is a major focus of gas turbine operation. Conventional Helmholtz resonators are an excellent means to attenuate thermoacoustic instabilities in gas turbines. Usually, however, the damping optimum is in a narrow frequency band at one operating condition. The work presented here deals with a modification of the basic Helmholtz resonator design over-coming this drawback. It consists of a damper body housing separated volumes that are connected to each other. Adequate adjustment of the governing parameters results in a broadband damping characteristic for low frequencies. In this way, changes in operating conditions and engine-to-engine variations involving shifts in the combustion pulsation frequency can conveniently be addressed. Genetic algorithms and optimization strategies are used to derive these parameters in a multi-dimensional parameter space. The novel damper concept is described in more detail and compared with cold-flow experiments. In order to validate the performance under realistic conditions, the new broadband dampers were implemented in a full-scale test engine. Pulsation amplitudes could be reduced by more than 80%. In addition, it is shown that due to sophisticated damper placement in the engine two unstable modes can be addressed simultaneously. Application of the damper concept allowed to considerably increase the engine operating regime and finally to reduce NOx emissions by 55%. Predictions obtained with the physics-based model excellently agree with experimental results for all tested damper geometries, bias flows, excitation amplitudes, and most important with the measurements in the engine.

Influence of Flame and Burner Transfer Matrix on Thermoacoustic Combustion Instability Modes and Frequencies

2010 ◽  
Author(s):  
Giovanni Campa ◽  
Sergio Mario Camporeale
Keyword(s):  
Heat Release ◽  
Combustion Chamber ◽  
Transfer Matrix ◽  
Acoustic Waves ◽  
Gas Turbines ◽  
Combustion Instability ◽  
Experimental Tests ◽  
Full Scale ◽  
Operating Conditions ◽  
Actual Geometry

The main origin of combustion instability in modern gas turbines is considered to be related to the interaction between acoustic waves and flame perturbations. An important role is played by the characteristics of combustion chamber and burners, because they influence the operating conditions at which the instability may occur. Experimental tests carried out on single burner arrangements fail to give adequate indications for the design of a full scale combustion chamber, due to the interaction of the local flame fluctuations with the propagation of the pressure waves, that have a wavelength of the same order of magnitude of the main dimensions of the chamber. Therefore there is a large interest on developing techniques able to make use of the data gathered from tests carried out on a single burner for predicting the thermoacoustic behavior of the combustion chamber at full scale with its actual geometry. A three dimensional finite element code has been developed for predicting acoustically driven combustion instabilities in combustion systems with complex geometries. The code allows one to identify the frequencies at which thermoacoustic instabilities are expected and the growth rate of the pressure oscillations, at the onset of instability, under the hypothesis of linear behaviour of the acoustic waves. The code permits to represent heat release fluctuations through an n–τ Flame Transfer Function (FTF) model and to adopt the transfer matrix method for modelling the burners. The FTF and the burner transfer matrix (BTM), as well as the temperature field and the flame location, needed for the simulation, can be obtained from experimental tests. Moreover, the code is able to make use of the local distribution of n and τ that can be evaluated from computational fluid dynamic studies on the single burner. The paper shows the importance of the flame characteristics, such as dimensions and shape of the heat release zone and its location within the combustor, underlying their influence on the instability of the modes and so the potential of the proposed method as a design tool for defining the burner characteristics and the acoustic impedance at the boundaries of the combustion chamber.

scholarly journals A Comparative Study on Fault Detection Methods for Gas Turbine Combustion Systems

Energies ◽  
2021 ◽  
Vol 14 (2) ◽  
pp. 389
Author(s):  
Jinfu Liu ◽  
Zhenhua Long ◽  
Mingliang Bai ◽  
Linhai Zhu ◽  
Daren Yu
Keyword(s):  
Fault Detection ◽  
Gas Turbine ◽  
Gas Turbines ◽  
Operating Conditions ◽  
Detection Methods ◽  
Distribution Model ◽  
Outlet Temperature ◽  
Combustion System ◽  
Comparison Results ◽  
Gas Turbine Combustion

As one of the core components of gas turbines, the combustion system operates in a high-temperature and high-pressure adverse environment, which makes it extremely prone to faults and catastrophic accidents. Therefore, it is necessary to monitor the combustion system to detect in a timely way whether its performance has deteriorated, to improve the safety and economy of gas turbine operation. However, the combustor outlet temperature is so high that conventional sensors cannot work in such a harsh environment for a long time. In practical application, temperature thermocouples distributed at the turbine outlet are used to monitor the exhaust gas temperature (EGT) to indirectly monitor the performance of the combustion system, but, the EGT is not only affected by faults but also influenced by many interference factors, such as ambient conditions, operating conditions, rotation and mixing of uneven hot gas, performance degradation of compressor, etc., which will reduce the sensitivity and reliability of fault detection. For this reason, many scholars have devoted themselves to the research of combustion system fault detection and proposed many excellent methods. However, few studies have compared these methods. This paper will introduce the main methods of combustion system fault detection and select current mainstream methods for analysis. And a circumferential temperature distribution model of gas turbine is established to simulate the EGT profile when a fault is coupled with interference factors, then use the simulation data to compare the detection results of selected methods. Besides, the comparison results are verified by the actual operation data of a gas turbine. Finally, through comparative research and mechanism analysis, the study points out a more suitable method for gas turbine combustion system fault detection and proposes possible development directions.

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.

Experimental Investigation of the Acoustic Reflection Coefficient of a Modeled Gas Turbine Impingement Cooling Section

2012 ◽  
Author(s):  
Christoph Jörg ◽  
Michael Wagner ◽  
Thomas Sattelmayer
Keyword(s):  
Reflection Coefficient ◽  
Flow Velocity ◽  
Gas Turbines ◽  
Acoustic Energy ◽  
Quality Data ◽  
Mean Flow ◽  
Impingement Cooling ◽  
Acoustic Reflection ◽  
The Mean ◽  
Mean Flow Velocity

The thermoacoustic stability of gas turbines depends on a balance of acoustic energy inside the engine. While the flames produce acoustic energy, other areas like the impingement cooling system contribute to damping. In this paper, we investigate the damping potential of an annular impingement sleeve geometry embedded into a realistic environment. A cold flow test rig was designed to represent real engine conditions in terms of geometry, and flow situation. High quality data was delivered by six piezoelectric dynamic pressure sensors. Experiments were carried out for different mean flow velocities through the cooling holes. The acoustic reflection coefficient of the impingement sleeve was evaluated at a downstream reference location. Further parameters investigated were the number of cooling holes, and the geometry of the chamber surrounding the impingement sleeve. Experimental results show that the determining parameter for the reflection coefficient is the mean flow velocity through the impingement holes. An increase of the mean flow velocity leads to significantly increased damping, and to low values of the reflection coefficient.

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