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Acoustic response of a helmholtz resonator exposed to hot-gas penetration and high amplitude oscillations / Bernhard Cosic in Transactions of the ASME . Journal of engineering for gas turbines and power, Vol. 134 N° 10 (Octobre 2012) 

Public ISBD [article]  in Transactions of the ASME . Journal of engineering for gas turbines and power > Vol. 134 N° 10 (Octobre 2012) . - 09 p. Titre : Acoustic response of a helmholtz resonator exposed to hot-gas penetration and high amplitude oscillations Type de document : texte imprimé Auteurs : Bernhard Cosic, Auteur ; Thoralf G. Reichel, Auteur ; Christian Oliver Paschereit, Auteur Année de publication : 2012 Article en page(s) : 09 p. Note générale : gas turbines Langues : Anglais (eng) Mots-clés : helmholtz  resonators;  thermoacoustic  instabilities;  hot-gas  intrusion Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : Helmholtz resonators are often used in the gas turbine industry for the damping of thermoacoustic instabilities. To prevent thermal destruction, these devices are usually cooled by a purging flow. Since the acoustic velocity inside the neck of the resonator becomes very high already at moderate pressure oscillation levels, hot-gas penetration cannot always be fully avoided. This study extends a well-known nonlinear impedance model to include the influence of hot-gas intrusion into the Helmholtz resonator neck. A time-dependent but spatially averaged density function of the volume flow in the neck is developed. The steady component of this density function is implemented into the nonlinear impedance model to account for the effect of hot-gas intrusion. The proposed model predicts a significant shift in the resonance frequency of the damper towards higher frequencies, depending on the amplitude of the acoustic velocity in the neck and the temperature of the penetrating hot gas. Subsequently, the model is verified by the experimental investigation of two resonance frequencies (86 Hz and 128 Hz) for two hot gas temperatures (1470 K and 570 K) and various pressure oscillation amplitudes. The multimicrophone method, in combination with a microphone flush-mounted in the resonator volume, is used to determine the impedance of the Helmholtz damper. Additionally, a movable ultra-thin thermocouple was used to determine the degree of hot-gas penetration and the change of the mean temperature at various axial positions in the neck. A very good agreement between the model and the experimental data is obtained for all levels of pressure amplitudes and of hot-gas penetration depths. The mean air temperatures in the neck were accurately predicted too. DEWEY : 620.1 ISSN : 0742-4795 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JETPEZ000134000010 [...] [article] Acoustic response of a helmholtz resonator exposed to hot-gas penetration and high amplitude oscillations [texte imprimé] / Bernhard Cosic, Auteur ; Thoralf G. Reichel, Auteur ; Christian Oliver Paschereit, Auteur . - 2012 . - 09 p. gas turbines Langues : Anglais (eng) in Transactions of the ASME . Journal of engineering for gas turbines and power > Vol. 134 N° 10 (Octobre 2012) . - 09 p. Mots-clés : helmholtz  resonators;  thermoacoustic  instabilities;  hot-gas  intrusion Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : Helmholtz resonators are often used in the gas turbine industry for the damping of thermoacoustic instabilities. To prevent thermal destruction, these devices are usually cooled by a purging flow. Since the acoustic velocity inside the neck of the resonator becomes very high already at moderate pressure oscillation levels, hot-gas penetration cannot always be fully avoided. This study extends a well-known nonlinear impedance model to include the influence of hot-gas intrusion into the Helmholtz resonator neck. A time-dependent but spatially averaged density function of the volume flow in the neck is developed. The steady component of this density function is implemented into the nonlinear impedance model to account for the effect of hot-gas intrusion. The proposed model predicts a significant shift in the resonance frequency of the damper towards higher frequencies, depending on the amplitude of the acoustic velocity in the neck and the temperature of the penetrating hot gas. Subsequently, the model is verified by the experimental investigation of two resonance frequencies (86 Hz and 128 Hz) for two hot gas temperatures (1470 K and 570 K) and various pressure oscillation amplitudes. The multimicrophone method, in combination with a microphone flush-mounted in the resonator volume, is used to determine the impedance of the Helmholtz damper. Additionally, a movable ultra-thin thermocouple was used to determine the degree of hot-gas penetration and the change of the mean temperature at various axial positions in the neck. A very good agreement between the model and the experimental data is obtained for all levels of pressure amplitudes and of hot-gas penetration depths. The mean air temperatures in the neck were accurately predicted too. DEWEY : 620.1 ISSN : 0742-4795 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JETPEZ000134000010 [...]

An experimental investigation of the nonlinear response of an atmospheric swirl-stabilized premixed flame / Sebastian Schimek in Transactions of the ASME . Journal of engineering for gas turbines and power, Vol. 133 N° 10 (Octobre 2011) 

Public ISBD [article]  in Transactions of the ASME . Journal of engineering for gas turbines and power > Vol. 133 N° 10 (Octobre 2011) . - 07 p. Titre : An experimental investigation of the nonlinear response of an atmospheric swirl-stabilized premixed flame Type de document : texte imprimé Auteurs : Sebastian Schimek, Auteur ; Jonas P. Moeck, Auteur ; Christian Oliver Paschereit, Auteur Année de publication : 2011 Article en page(s) : 07 p. Note générale : Génie mécanique Langues : Anglais (eng) Mots-clés : Acoustic  field  Chemiluminescence  Combustion  Flames  Gas  turbines  Natural  gas  technology Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : Due to stringent emission restrictions, modern gas turbines mostly rely on lean premixed combustion. Since this combustion mode is susceptible to thermoacoustic instabilities, there is a need for modeling tools with predictive capabilities. Linear network models are able to predict the occurrence of thermoacoustic instabilities but yield no information on the oscillation amplitude. The prediction of the pulsation levels and hence an estimation whether a certain operating condition has to be avoided is only possible if information on the nonlinear flame response is available. Typically, the flame response shows saturation at high forcing amplitudes. A newly constructed atmospheric test rig, specifically designed for the realization of high excitation amplitudes over a broad frequency range, is used to generate extremely high acoustic forcing power with velocity fluctuations of up to 100% of the mean flow. The test rig consists of a generic combustor with a premixed swirl-stabilized natural gas flame, where the upstream part has a variable length to generate adaptive resonances of the acoustic field. The OH* chemiluminescence response, with respect to velocity fluctuations at the burner, is measured for various excitation frequencies and amplitudes. From these measurements, an amplitude dependent flame transfer function is obtained. Phase-averaged OH* pictures are used to identify changes in the flame shape related to saturation mechanisms. For different frequency regimes, different saturation mechanisms are identified. DEWEY : 620.1 ISSN : 0742-4795 En ligne : http://asmedl.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JETPEZ00013300 [...] [article] An experimental investigation of the nonlinear response of an atmospheric swirl-stabilized premixed flame [texte imprimé] / Sebastian Schimek, Auteur ; Jonas P. Moeck, Auteur ; Christian Oliver Paschereit, Auteur . - 2011 . - 07 p. Génie mécanique Langues : Anglais (eng) in Transactions of the ASME . Journal of engineering for gas turbines and power > Vol. 133 N° 10 (Octobre 2011) . - 07 p. Mots-clés : Acoustic  field  Chemiluminescence  Combustion  Flames  Gas  turbines  Natural  gas  technology Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : Due to stringent emission restrictions, modern gas turbines mostly rely on lean premixed combustion. Since this combustion mode is susceptible to thermoacoustic instabilities, there is a need for modeling tools with predictive capabilities. Linear network models are able to predict the occurrence of thermoacoustic instabilities but yield no information on the oscillation amplitude. The prediction of the pulsation levels and hence an estimation whether a certain operating condition has to be avoided is only possible if information on the nonlinear flame response is available. Typically, the flame response shows saturation at high forcing amplitudes. A newly constructed atmospheric test rig, specifically designed for the realization of high excitation amplitudes over a broad frequency range, is used to generate extremely high acoustic forcing power with velocity fluctuations of up to 100% of the mean flow. The test rig consists of a generic combustor with a premixed swirl-stabilized natural gas flame, where the upstream part has a variable length to generate adaptive resonances of the acoustic field. The OH* chemiluminescence response, with respect to velocity fluctuations at the burner, is measured for various excitation frequencies and amplitudes. From these measurements, an amplitude dependent flame transfer function is obtained. Phase-averaged OH* pictures are used to identify changes in the flame shape related to saturation mechanisms. For different frequency regimes, different saturation mechanisms are identified. DEWEY : 620.1 ISSN : 0742-4795 En ligne : http://asmedl.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JETPEZ00013300 [...]

Application of fiber-optical microphone for thermo-acoustic measurements / Holger J. Konle in Transactions of the ASME . Journal of engineering for gas turbines and power, Vol. 133 N° 1 (Janvier 2011) 

Public ISBD [article]  in Transactions of the ASME . Journal of engineering for gas turbines and power > Vol. 133 N° 1 (Janvier 2011) . - 08 p. Titre : Application of fiber-optical microphone for thermo-acoustic measurements Type de document : texte imprimé Auteurs : Holger J. Konle, Auteur ; Christian Oliver Paschereit, Auteur ; Ingo Röhle, Auteur Année de publication : 2012 Article en page(s) : 08 p. Note générale : Génie Mécanique Langues : Anglais (eng) Mots-clés : Acoustic  measurement  Acoustic  wave  interferometry  Fibre  optic  sensors  Microphones Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : A high temperature resistant fiber-optical microphone (FOM) was developed and successfully applied in a combustion chamber at a thermal power of 8.4 kW to measure thermo-acoustic oscillations at a frequency of 85 Hz and a sound pressure level of 154 dB. The sensor head temperature was estimated to ~1000 K. The core of the optical setup used for the FOM is a Fabry–Perot interferometer. To create an acoustical sensor based on this type of interferometer, a new method of generation and postprocessing of the interference signal was developed. The simple replaceability of the sensor membrane reduces the requirements concerning the sensor handling compared with conventional condenser microphones and allows the adaptation of the sensor sensitivity to its application case changing the membrane stiffness. DEWEY : 620.1 ISSN : 0742-4795 En ligne : scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JETPEZ000133000001 [...] [article] Application of fiber-optical microphone for thermo-acoustic measurements [texte imprimé] / Holger J. Konle, Auteur ; Christian Oliver Paschereit, Auteur ; Ingo Röhle, Auteur . - 2012 . - 08 p. Génie Mécanique Langues : Anglais (eng) in Transactions of the ASME . Journal of engineering for gas turbines and power > Vol. 133 N° 1 (Janvier 2011) . - 08 p. Mots-clés : Acoustic  measurement  Acoustic  wave  interferometry  Fibre  optic  sensors  Microphones Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : A high temperature resistant fiber-optical microphone (FOM) was developed and successfully applied in a combustion chamber at a thermal power of 8.4 kW to measure thermo-acoustic oscillations at a frequency of 85 Hz and a sound pressure level of 154 dB. The sensor head temperature was estimated to ~1000 K. The core of the optical setup used for the FOM is a Fabry–Perot interferometer. To create an acoustical sensor based on this type of interferometer, a new method of generation and postprocessing of the interference signal was developed. The simple replaceability of the sensor membrane reduces the requirements concerning the sensor handling compared with conventional condenser microphones and allows the adaptation of the sensor sensitivity to its application case changing the membrane stiffness. DEWEY : 620.1 ISSN : 0742-4795 En ligne : scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JETPEZ000133000001 [...]

Comparison of linear stability analysis with experiments by actively tuning the acoustic boundary conditions of a premixed combustor / Mirko R. Bothien in Transactions of the ASME . Journal of engineering for gas turbines and power, Vol. 132 N° 12 (Décembre 2010) 

Public ISBD [article]  in Transactions of the ASME . Journal of engineering for gas turbines and power > Vol. 132 N° 12 (Décembre 2010) . - 10 p. Titre : Comparison of linear stability analysis with experiments by actively tuning the acoustic boundary conditions of a premixed combustor Type de document : texte imprimé Auteurs : Mirko R. Bothien, Auteur ; Jonas P. Moeck, Auteur ; Christian Oliver Paschereit, Auteur Année de publication : 2011 Article en page(s) : 10 p. Note générale : Génie Mécanique Langues : Anglais (eng) Mots-clés : Acoustic  analysis  Combustion  Flow  instability  Stability  Swirling  flow  Test  equipment  Thermoacoustics Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : Linear stability analysis by means of low-order network models is widely spread in industry and academia to predict the thermoacoustic characteristics of combustion systems. Even though a vast amount of publications on this topic exist, much less is reported on the predictive capabilities of such stability analyses with respect to real system behavior. In this sense, little effort has been made on investigating if predicted critical parameter values, for which the combustion system switches from stability to instability, agree with experimental observations. Here, this lack of a comprehensive experimental validation is addressed by using a model-based control scheme. This scheme is able to actively manipulate the acoustic field of a combustion test rig by imposing quasi-arbitrary reflection coefficients. It is employed to continuously vary the downstream reflection coefficient of an atmospheric swirl-stabilized combustion test rig from fully reflecting to anechoic. By doing so, the transient behavior of the system can be studied. In addition to that, an extension of the common procedure, where the stability of an operating point is classified solely based on the presence of high amplitude pressure pulsations and their frequency, is given. Generally, the predicted growth rates are only compared with measurements with respect to their sign, which obviously lacks a quantitative component. In contrast to that, in this paper, validation of linear stability analysis is conducted by comparing calculated and experimentally determined linear growth rates of unstable modes. Besides this, experimental results and model predictions are also compared in terms of frequency of the least stable mode. Excellent agreement between computations from the model and experiments is found. The concept is also used for active control of combustion instabilities. By tuning the downstream reflectivity of the combustion test rig, thermoacoustic instabilities can be suppressed. The underlying mechanism is an increase in the acoustic energy losses across the system boundary. DEWEY : 620.1 ISSN : 0742-4795 En ligne : http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JETPEZ00013 [...] [article] Comparison of linear stability analysis with experiments by actively tuning the acoustic boundary conditions of a premixed combustor [texte imprimé] / Mirko R. Bothien, Auteur ; Jonas P. Moeck, Auteur ; Christian Oliver Paschereit, Auteur . - 2011 . - 10 p. Génie Mécanique Langues : Anglais (eng) in Transactions of the ASME . Journal of engineering for gas turbines and power > Vol. 132 N° 12 (Décembre 2010) . - 10 p. Mots-clés : Acoustic  analysis  Combustion  Flow  instability  Stability  Swirling  flow  Test  equipment  Thermoacoustics Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : Linear stability analysis by means of low-order network models is widely spread in industry and academia to predict the thermoacoustic characteristics of combustion systems. Even though a vast amount of publications on this topic exist, much less is reported on the predictive capabilities of such stability analyses with respect to real system behavior. In this sense, little effort has been made on investigating if predicted critical parameter values, for which the combustion system switches from stability to instability, agree with experimental observations. Here, this lack of a comprehensive experimental validation is addressed by using a model-based control scheme. This scheme is able to actively manipulate the acoustic field of a combustion test rig by imposing quasi-arbitrary reflection coefficients. It is employed to continuously vary the downstream reflection coefficient of an atmospheric swirl-stabilized combustion test rig from fully reflecting to anechoic. By doing so, the transient behavior of the system can be studied. In addition to that, an extension of the common procedure, where the stability of an operating point is classified solely based on the presence of high amplitude pressure pulsations and their frequency, is given. Generally, the predicted growth rates are only compared with measurements with respect to their sign, which obviously lacks a quantitative component. In contrast to that, in this paper, validation of linear stability analysis is conducted by comparing calculated and experimentally determined linear growth rates of unstable modes. Besides this, experimental results and model predictions are also compared in terms of frequency of the least stable mode. Excellent agreement between computations from the model and experiments is found. The concept is also used for active control of combustion instabilities. By tuning the downstream reflectivity of the combustion test rig, thermoacoustic instabilities can be suppressed. The underlying mechanism is an increase in the acoustic energy losses across the system boundary. DEWEY : 620.1 ISSN : 0742-4795 En ligne : http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JETPEZ00013 [...]

Effects of outlet boundary conditions on the reacting flow field in a swirl-stabilized burner at dry and humid conditions / Steffen Terhaar in Transactions of the ASME . Journal of engineering for gas turbines and power, Vol. 134 N° 11 (Novembre 2012) 

Public ISBD [article]  in Transactions of the ASME . Journal of engineering for gas turbines and power > Vol. 134 N° 11 (Novembre 2012) . - 09 p. Titre : Effects of outlet boundary conditions on the reacting flow field in a swirl-stabilized burner at dry and humid conditions Type de document : texte imprimé Auteurs : Steffen Terhaar, Auteur ; Bernhard C. Bobusch, Auteur ; Christian Oliver Paschereit, Auteur Année de publication : 2012 Article en page(s) : 09 p. Note générale : gas turbines Langues : Anglais (eng) Mots-clés : swirl-stabilized  combustors;  outlet  boundary  conditions;  reacting  flow  field Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : During the design and testing process of swirl-stabilized combustors, it is often impractical to maintain identical outlet boundary conditions. Furthermore, it is a common practice to intentionally change the acoustic boundary conditions of the outlet in order to suppress thermoacoustic instabilities. In the presented work the susceptibility of the reacting flow field to downstream perturbations is assessed by the application of an area contraction at the outlet. Since combustion and fuel composition are shown to be important parameters for the influence of the boundary conditions on the flow field, highly steam diluted flames are investigated in addition to dry flames at different equivalence ratios and degrees of swirl. The applied measurement techniques include particle image velocimetry, laser doppler velocimetry, and emission analysis. The results reveal a clear correlation of the susceptibility of the flow field to downstream perturbations to both the inlet swirl number and the amount of dilatation caused by the flame. The concept of an effective swirl number downstream of the flame is applied to the results and is proven to be the dominating parameter. A theoretical explanation for the influence of this parameter is provided by the usage of the well known theory of subcritical and supercritical swirling flows, where perturbations can propagate upstream solely in subcritical flows via standing waves. Knowledge of the flow state is of particular importance for the evaluation of combustion tests with differing exit boundary conditions and the results emphasize the need for realistic exit boundary conditions for numerical simulations. DEWEY : 620.1 ISSN : 0742-4795 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JETPEZ000134000011 [...] [article] Effects of outlet boundary conditions on the reacting flow field in a swirl-stabilized burner at dry and humid conditions [texte imprimé] / Steffen Terhaar, Auteur ; Bernhard C. Bobusch, Auteur ; Christian Oliver Paschereit, Auteur . - 2012 . - 09 p. gas turbines Langues : Anglais (eng) in Transactions of the ASME . Journal of engineering for gas turbines and power > Vol. 134 N° 11 (Novembre 2012) . - 09 p. Mots-clés : swirl-stabilized  combustors;  outlet  boundary  conditions;  reacting  flow  field Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : During the design and testing process of swirl-stabilized combustors, it is often impractical to maintain identical outlet boundary conditions. Furthermore, it is a common practice to intentionally change the acoustic boundary conditions of the outlet in order to suppress thermoacoustic instabilities. In the presented work the susceptibility of the reacting flow field to downstream perturbations is assessed by the application of an area contraction at the outlet. Since combustion and fuel composition are shown to be important parameters for the influence of the boundary conditions on the flow field, highly steam diluted flames are investigated in addition to dry flames at different equivalence ratios and degrees of swirl. The applied measurement techniques include particle image velocimetry, laser doppler velocimetry, and emission analysis. The results reveal a clear correlation of the susceptibility of the flow field to downstream perturbations to both the inlet swirl number and the amount of dilatation caused by the flame. The concept of an effective swirl number downstream of the flame is applied to the results and is proven to be the dominating parameter. A theoretical explanation for the influence of this parameter is provided by the usage of the well known theory of subcritical and supercritical swirling flows, where perturbations can propagate upstream solely in subcritical flows via standing waves. Knowledge of the flow state is of particular importance for the evaluation of combustion tests with differing exit boundary conditions and the results emphasize the need for realistic exit boundary conditions for numerical simulations. DEWEY : 620.1 ISSN : 0742-4795 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JETPEZ000134000011 [...]

Increasing the passive scalar mixing quality of jets in crossflow with fluidics actuators / Arnaud Lacarelle in Transactions of the ASME . Journal of engineering for gas turbines and power, Vol. 134 N° 2 (Février 2012) 

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Tuning of the acoustic boundary conditions of combustion test rigs with active control / Mirko R. Bothien in Transactions of the ASME . Journal of engineering for gas turbines and power, Vol. 132 N° 9 (Septembre 2010) 

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