Optical whispering gallery microcavities with high-quality factors have shown great potential toward achieveing ultrahigh-sensitivity sensing up to a single molecule or nanoparticle, which raises a huge demand on a de...Optical whispering gallery microcavities with high-quality factors have shown great potential toward achieveing ultrahigh-sensitivity sensing up to a single molecule or nanoparticle, which raises a huge demand on a deep theoretical insight into the crucial phenomena such as the mode shift, mode splitting, and mode broadening in sensing experiments. Here we propose an intuitive model to analyze these phenomena from the viewpoint of the nanoparticle-induced multiple scattering of the azimuthally propagating mode(APM). The model unveils explicit relations between these phenomena and the phase change and energy loss of the APM when scattered at the nanoparticle; the model also explains the observed polarization-dependent preservation of one resonance and the particle-dependent redshift or blueshift. The model indicates that the particle-induced coupling between the pair of unperturbed degenerate whispering gallery modes(WGMs) and the coupling between the WGMs and the free-space radiation modes, which are widely adopted in current theoretical formalisms, are realized via the reflection and scattering-induced free-space radiation of the APM, respectively, and additionally exhibits the contribution of cross coupling between the unperturbed WGMs and other different WGMs to forming the splittingresonant modes, especially for large particles.展开更多
Dual-volume Helmholtz dampers with two resonant frequencies are proposed to simultaneously attenuate longitudinal and azimuthal thermo-acoustic instabilities in annular combustors. Thermo-acoustic instabilities in a s...Dual-volume Helmholtz dampers with two resonant frequencies are proposed to simultaneously attenuate longitudinal and azimuthal thermo-acoustic instabilities in annular combustors. Thermo-acoustic instabilities in a swirled annular combustor equipped with dual-volume dampers are numerically investigated by the Helmholtz method, combined with a measured flame transfer function and the established damper impedance model. Furthermore, the influences of the damper number and circumferential configurations on oscillation attenuations and mode structures are explored. The established dual-volume damper model is well validated by the impedance tube tests. Numerical results indicate velocity fluctuation levels of the longitudinal and azimuthal modes decline after installing Helmholtz dampers, whereas those of the azimuthal modes further decrease by around 16% after using four retuned dual-volume dampers. The eigenfrequencies of the first longitudinal and azimuthal modes decrease and increase after installing dampers, respectively. After installing dual-volume dampers, the difference between the pressure fluctuation in the plenum and combustion chamber is reduced, and pressure waveforms of the azimuthal modes along the circumferential direction shifts. The pressure distribution of azimuthal modes becomes more uniform after using more dual-volume dampers. The specific absorption frequency band for azimuthal modes introduced by the dual-volume damper may lead to decreased oscillations and mode evolutions. The maximal absorbing ability can be approached by installing dampers with the same angle between adjacent dampers. When dampers are unevenly distributed, the symmetry between two azimuthal modes is broken and standing modes will emerge.展开更多
基金National Key Basic Research Program of China(2013CB328701)National Natural Science Foundation of China(NSFC)(61322508,11504270)
文摘Optical whispering gallery microcavities with high-quality factors have shown great potential toward achieveing ultrahigh-sensitivity sensing up to a single molecule or nanoparticle, which raises a huge demand on a deep theoretical insight into the crucial phenomena such as the mode shift, mode splitting, and mode broadening in sensing experiments. Here we propose an intuitive model to analyze these phenomena from the viewpoint of the nanoparticle-induced multiple scattering of the azimuthally propagating mode(APM). The model unveils explicit relations between these phenomena and the phase change and energy loss of the APM when scattered at the nanoparticle; the model also explains the observed polarization-dependent preservation of one resonance and the particle-dependent redshift or blueshift. The model indicates that the particle-induced coupling between the pair of unperturbed degenerate whispering gallery modes(WGMs) and the coupling between the WGMs and the free-space radiation modes, which are widely adopted in current theoretical formalisms, are realized via the reflection and scattering-induced free-space radiation of the APM, respectively, and additionally exhibits the contribution of cross coupling between the unperturbed WGMs and other different WGMs to forming the splittingresonant modes, especially for large particles.
基金funded by the National Science and Technology Major Project(J2019-Ⅲ-0020-0064)。
文摘Dual-volume Helmholtz dampers with two resonant frequencies are proposed to simultaneously attenuate longitudinal and azimuthal thermo-acoustic instabilities in annular combustors. Thermo-acoustic instabilities in a swirled annular combustor equipped with dual-volume dampers are numerically investigated by the Helmholtz method, combined with a measured flame transfer function and the established damper impedance model. Furthermore, the influences of the damper number and circumferential configurations on oscillation attenuations and mode structures are explored. The established dual-volume damper model is well validated by the impedance tube tests. Numerical results indicate velocity fluctuation levels of the longitudinal and azimuthal modes decline after installing Helmholtz dampers, whereas those of the azimuthal modes further decrease by around 16% after using four retuned dual-volume dampers. The eigenfrequencies of the first longitudinal and azimuthal modes decrease and increase after installing dampers, respectively. After installing dual-volume dampers, the difference between the pressure fluctuation in the plenum and combustion chamber is reduced, and pressure waveforms of the azimuthal modes along the circumferential direction shifts. The pressure distribution of azimuthal modes becomes more uniform after using more dual-volume dampers. The specific absorption frequency band for azimuthal modes introduced by the dual-volume damper may lead to decreased oscillations and mode evolutions. The maximal absorbing ability can be approached by installing dampers with the same angle between adjacent dampers. When dampers are unevenly distributed, the symmetry between two azimuthal modes is broken and standing modes will emerge.
