燃烧振荡声学抑制器的机理分析与设计优化

Mechanism and design optimization of acoustic dampers for attenuating combustion instabilities

燃烧振荡是发展低排放燃气轮机燃烧室需要解决的关键问题之一,未来燃气轮机燃烧室运行温度更高、具有更宽的工况运行范围及更复杂的几何结构(如轴向分级、环形燃烧室等),燃烧振荡存在高振幅、多振荡频率、多振荡频率时变和多热声模态共存等特点。采用声学抑制器被动控制燃烧振荡具有抑制器结构简单、可靠性高、成本较低等优势。针对未来的燃烧室,现有抑制器方案将面临很大挑战,因此,亟需开展宽吸声带宽、可控制多模态的声学抑制器及系统级燃烧室多声学抑制器设计优化研究。该文概述了国内外声学抑制器机理和设计优化的研究进展,着重总结了作者近年来在常规及多频段声学抑制器机理、抑制效果分析计算和复杂热声系统参数对声学抑制器特性影响,以及基于伴随方法的多声学抑制器多参数快速优化等方面的研究工作,并对未来燃烧室声学抑制器的发展方向进行了讨论。

[Significance]Combustion instability is a crucial issue in developing low-emission gas turbine combustors.Meanwhile,future combustors will possess higher temperatures,wider operation parameter ranges,and more complicated geometric structures(e.g.,axially staged and annular).Thus,combustion instabilities have the features of high amplitude levels,multiple and time-varying frequencies,and the coexistence of several modes.Passive control employing acoustic dampers for attenuating oscillations has many advantages,such as simple structures,high reliabilities,and low costs.However,the present damper designs encounter great challenges for future combustors.Therefore,multimode wide-absorption acoustic dampers and systematic design optimization methods for multiple dampers must be investigated.[Progress]This paper briefly reviewed the research progress of mechanisms and optimization methods for acoustic dampers and the recent corresponding work conducted by the authors.First,the mechanisms for conventional and multi-bandwidth acoustic dampers were analyzed.Previous acoustic models for holes assumed that the thickness is ignorable and two open ends are inserted into semi-infinite space.A novel semianalytic acoustic model for short holes was proposed to consider sound-vortex interactions in detail.Sound generation and absorption can be well predicted by this model.Additionally,the performance of holes was sensitive to the shape of the hole edges.To broaden the absorption bandwidth of the Helmholtz resonators,parallel perforated materials were installed at the neck of the resonators.A theoretical model was derived to calculate the sound absorption coefficient of this type of resonator and effectively captured the nonlinear effect at the neck.Traditional resonators only possess a single frequency band for suppressing instabilities.Two multi-bandwidth resonators based on elastic membranes and multiple cavities were proposed by the authors.The results showed that elastic membranes and multiple cavities may introduce new frequency bands.Meanwhile,a low-order network model coupled with nonlinear flame dynamics and the acoustic models of resonators was developed to successfully predict thermoacoustic instabilities in cylindrical and annular combustors.The stability of annular combustors could be affected by the asymmetrical flame responses after introducing acoustic resonators.Subsequently,we examined the effects of complex thermoacoustic parameters on the acoustic characteristics of resonators and optimization strategies for designing multiple resonators.A theoretical model combined with the energy equation was established to explore the effect of a temperature difference on resonator performances.The results showed that the entropy disturbance caused by large temperature differences could affect the thermoacoustic stabilities of combustors.The cross-section of resonators was another critical factor in influencing the resonator properties.The acoustic characteristics of perforated liners with variable cross sections were theoretically and experimentally explored.Decreasing the cross-section increased the range of absorption frequency bands.The introduction of resonators for suppressing thermoacoustic instabilities changes the acoustic modes of combustors and the intrinsic modes of flames.An available strategy considering these influences was determined for reasonably designing the resonators.There are many adjustable parameters when multiple resonators are employed simultaneously.An efficient multiparameter adjoint-based optimization strategy for multiple resonators was developed.This algorithm is based on treating the low-order network model by performing the adjoint method.[Conclusions and Prospects]The next generation of multimode wide-absorption acoustic resonators urgently needs to be explored.Moreover,the effects and mechanisms of nonlinearity,mean flow,temperature difference,and other complex physical parameters on the properties of acoustic resonators need to be further explored.Meanwhile,the effectiveness and robustness of current optimization strategies for designing multiple resonators must be improved.