旋流数对燃烧不稳定性及NOx生成的影响

摘要

Effects of swirl number on premixed combustion instability and NOx formation characteristics in combustion chamber of a gas turbine were numerically studied using large eddy simulation technology.Results show that increasing the swirl number would expand the divergence angle of flow field,enlarge the center recirculation zone,enhance the recirculation process of hot products,raise the temperature in premixing area and broaden the high-temperature zone,which are favourable for the ignition and stable combustion of fuel flow as well as for the shortening of flame length;there is a single processing vortex core (PVC) in the flow field under the swirl number of 0.7,and another PVC would occur under higher swirl numbers;increasing the swirl number would improve the periodic shedding frequency of vortex and make the crush position of PVC move towards upstream,when both the oscillation frequency and amplitude of pressure would be improved due to the shortened flame length and concentrated heat release region;increasing the swirl number would also expand the flame width and reduce the peak value of temperature,which are favourable for the control of NOx emission.%采用大涡模拟方法分析了旋流数对燃气轮机燃烧室内预混燃烧不稳定性以及NOx生成特性的影响.结果表明:增大旋流数使得流场的扩张角增大,中心回流区范围扩大,对燃烧产物的卷吸能力增强,预混段内温度升高,高温区范围扩大,有利于燃料气流的着火与稳定燃烧,火焰长度也有所缩短;旋流数为0.7时,流场中仅存在一个进动涡核,旋流数较大时,则出现2个明显的进动涡核;增大旋流数使得涡旋周期性的脱落频率增加,破碎位置向上游移动,同时由于火焰长度缩短,热释放区域相对更为集中,从而导致燃烧室内压力脉动频率及其对应的压力峰值增大;增大旋流数也使得火焰宽度增大,峰值温度有所降低,有利于控制NOx排放体积分数.