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]  inTransactions 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 [...]

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