亥姆霍兹共振器对热声不稳定极限环的预测

Prediction of Helmholtz dampers on limit cycle of thermoacoustic instabilities

验证亥姆霍兹法求解亥姆霍兹共振器对热声极限环影响的可靠性,实验在Rijke管上进行。采用耦合非线性热释放率模型、实测阻尼率及共振器阻抗模型的亥姆霍兹法求解耦合共振器前后热声极限环特性。其中共振器阻抗模型采用阻抗管修正。结果表明:修正的阻抗模型可有效模拟不同背腔流量下共振器反射率幅值和相位。背腔流量增加,共振器阻抗增加。未加共振器,85 V加热电压模拟的极限环频率和速度振幅相对误差为3.4%和7.2%。耦合共振器,低背腔流量,预测的极限环频率和速度振幅相对误差为3.7%和6.2%。背腔流量越大,共振器接口涡脱落增强,减振效果增强,但采用忽略流动的亥姆霍兹法模拟精度降低。共振器安装位置离波腹越近,减振效果越好。

Whether Helmholtz method can be used to predict the effects of Helmholtz damper on thermoacoustic limit cycle was investigated. Corresponding experimental validations were performed in a Rijke tube. The limit cycle properties of the Rijke tube equipped with a damper were calculated by the Helmholtz equation coupled with nonlinear heat release model, impedance model and damping rate. The impedance model of the damper was validated in an impedance tube. Results showed that the reflection coefficients of dampers could be calculated by the modified impedance model. The impedance increased with the purge mass flow. Without dampers, the relative errors of predicted limit cycle eigen-frequency and velocity amplitude were 3.4% and 7.2% at the heating voltage of 85 V, respectively. With dampers, the calculated maximum relative errors of those were 3.7% and 6.2%, respectively, under low mass flow. This passive control can be enhanced by increasing purge mass flow due to the vortex shedding. It is advisable to install the damper close to the pressure antinodes.