不同冷却边界下燃烧室受迫振荡特性

Investigation of combustor-forced instability under different cooling boundaries

为考察冷却边界对燃烧室受迫振荡特性的影响规律,该文通过试验与声模态计算相结合的方法,对比了冲击冷却边界和发散冷却边界对燃烧室内声压脉动特性的影响,探究了吹风比改变对发散冷却边界声学特性的影响。结果表明:发散冷却边界具有明显的吸声作用,发散冷却边界下燃烧室内声压脉动幅值相比于冲击冷却边界降幅最大达37.7%;发散冷却边界吸声能力与扰动频率相关,当扰动频率低于90 Hz或高于170 Hz时发散冷却边界吸声能力降低。此外,发散冷却边界在无冷气流动时吸声能力最优,吹风比增大会使发散冷却边界吸声能力明显降低。

[Objective]Suppression of combustion oscillations is critical to the design of aero engines and gas turbine combustion chambers to avoid materials and structural damage caused by structural resonance and to prevent the reduction of combustion effectiveness.Previous research has shown that adjustments in common wall cooling methods,such as effusion cooling,can affect the acoustic properties of combustion chambers and can be considered in the design to inhibit instability.However,these previous studies mainly operate under non-reaction conditions,ignoring the mutual interference between flow,flame heat release,coolant flow,and sound oscillation.Therefore,the results deviate from actual engine operating states and need to be verified under reaction conditions.[Methods]This study investigated the influence of effusion and impingement cooling boundaries on forced oscillation characteristics.A swirl-stabilized model combustor test rig with a boundary of effusion/impingement cooling structure was built,and its acoustic characteristics are measured by microphone sensors.The influence of effusion and impingement cooling boundaries on the pressure pulsation with an excitation frequency of 80~210 Hz of a model combustion chamber is compared using experimental and acoustic numerical methods under the same reacting conditions of a ratio equivalent to 0.61.In the acoustic simulations,we examine the acoustic principle of why the effusion cooling boundary has a better performance in sound absorption compared with the impingement cooling boundary.In addition,the blowing ratio of effusion cooling is then changed to 0~8 to determine the influence of coolant mass flow change on its sound absorption ability.[Results](1)Experimental and numerical investigations indicated that the effusion cooling boundary has better sound absorption ability in the pressure oscillation than the impingement cooling boundary,and the amplitude of sound pressure pulsation in the combustion chamber decreased at the largest percent of 37.7%at an excitation frequency of 110 Hz.(2)Changes in the upstream excitation frequency revealed its relationship to the sound absorption capacity of the effusion cooling boundary.Within a pulsation frequency band of 90~170 Hz,the absorption ability of the effusion cooling structure can lead to lower pressure pulsation amplitude.However,when the excitation frequency is<90 Hz or>170 Hz,the sound absorption capacity sharply decreased,and the pressure oscillation amplitude of the effusion-cooled combustor became similar to the impingement cooling boundary.(3)Changes in the blowing ratio(BR)in the effusion cooling boundary are proved to influence its sound absorption capacity.The effusion cooling boundary achieved the best sound absorption ability when BR is 0,owing to the pulsation energy consumption ability of the tiny holes.However,with the increase in BR,the pressure oscillation amplitude increased because of the noise caused by the coolant passing through the tiny holes,while the sound transmission capacity decreased owing to increased back pressure.[Conclusions]The effusion cooling boundary shows a better performance in suppressing combustion instability,especially in the frequency band of 90~170 Hz,and can achieve better sound absorption ability through its BR adjustment.