旋流预混燃烧室火焰描述函数分析及其自激热声计算

Analysis of Flame Describing Functions in a Swirled Premixed Combustor and Calculation for Self-Excited Thermo-Acoustic Instabilities

关键词:  热声不稳定  火焰描述函数  旋流预混火焰  运行参数  亥姆霍兹法  数值预测

Key words:  Thermo-acoustic instability  Flame describing function  Swirled premixed flame  Operating conditions  Helmholtz method  Numerical prediction

摘要:

为考察运行参数对火焰描述函数的影响，及验证结合火焰描述函数的燃烧室热声不稳定数值预测方法可行性，测量了一燃气轮机典型旋流部分预混火焰不同运行参数下的火焰描述函数，并结合该实测火焰描述函数及热态阻尼率，采用亥姆霍兹法数值预测了燃烧室自激热声振荡参数。结果表明，该旋流部分预混火焰的火焰描述函数具有低通和带通增益峰，随激励振幅增加，增益不断降低；相位值与频率基本呈线性关系。当量比较低时，火焰描述函数主要呈现火焰拉伸效应引起的低通增益峰；随当量比增加，低通增益逐渐减弱，涡脱落效应引起的带通增益峰逐渐加强。随空气流量增加，火焰描述函数高增益频率带明显拓宽，而高增益对应的施特劳哈尔数St边界变化较小，增益峰均位于St=0.23和0.80附近。结合实测火焰描述函数、热态有火焰下阻尼率及温度分布，亥姆霍兹法数值预测的特征频率相对误差约10%，速度振幅比绝对误差在0.05以下。

Abstract:

In order to investigate the effects of operating conditions on flame describing functions and validate the numerical method combined with these flame describing functions for predicting thermoacoustic instabilities， flame describing functions of a typical swirled partially premixed flame in gas turbine combustors were experimentally measured. Combining measured flame describing functions and damping rates under the firing condition， the Helmholtz method was performed to predict self-excited thermo-acoustic oscillations in the combustor. Results indicated that flame describing functions of this swirled premixed flame displayed low-pass and band-pass gain peaks. The gains of flame describing functions decreased with the increase of the excited velocity amplitude. The phases were appropriately proportional to the frequency. When the equivalence ratio maintained a low value， the flame describing function showed a low-pass gain peak caused by the flame stretch. With the increase of the equivalence ratio， low-pass gains declined and band-pass gains gradually raised due to the enhanced vortex shedding. As the air volume flow rate increased， the frequency band with high gains was significantly broadened， while the corresponding boundary of Strouhal number（St）was slightly changed. The corresponding gain peaks were located at St=0.23 and 0.80. Combining measured flame describing functions， damping rates under the firing condition and temperature distributions， relative errors of eigenfrequencies predicted by the Helmholtz method were around 10% and absolute errors of predicted velocity fluctuation levels were below 0.05.