摘要
为了更好地理解航空发动机燃烧室内的旋流预混燃烧现象和机理,基于相关特征参数采用直接数值模拟方法研究了模型燃烧室内的旋流预混火焰。其中计算模型简化自环形燃烧室,包含两个相邻的贫燃旋流,参数尽可能接近实际航空发动机燃烧室工况。模拟中,采用了简化的煤油反应机理,设计了不同Karlovitz数(Ka)对应高低两种负荷。结果表明,在高压下火焰面极薄,小尺度湍流扰动对火焰面影响显著,燃烧室内湍流预混火焰位于薄反应区。在下游由于相邻旋流的作用而产生较为破碎的火焰结构,这一现象在高Ka时尤为明显。雷诺数Re和Ka较大时,旋流剪切作用所导致的下游中心回流效应增强,剪切层中的湍流扰动效应也更强。航空发动机燃烧室内主要反应物和生成物基本满足梯度输运关系,且在Ka较大时,梯度输运效应更显著。然而对于中间产物,梯度扩散假设在火焰面附近不成立,这对基于梯度扩散假设的相关计算模型提出了挑战。
In order to better understand the turbulent premixed combustion in aero-engine combustors,the turbulent premix flames in model combustors were studied by direct numerical simulations based on the relevant characteristic parameters.The calculation model is simplified from annular combustors that contains two adjacent lean premixed swirls with high inlet temperature and pressure to meet the aero-engine combustor conditions.In the simulation,the simplified kerosene reaction mechanism was used and different Karlovitz numbers(Ka)were designed corresponding to high and low loads.The simulation results show that the flame thickness under high pressure is extremely thin,so the flame surface is strongly affected by small scale turbulence.The turbulent premixed flame is located at thin reaction zone,which is distributed bilaterally along the shear layer,and a relatively broken flame structure is generated in the downstream due to the interaction of adjacent swirls,which is especially obvious when the Kais high.From the upstream to the downstream,the average radial velocity increases due to the combustion expansion,while the average azimuthal velocity decreases due to the conservation of angular momentum.Turbulence pulsation in the downstream recirculation zone is stronger than that in the upstream.When the Re and Ka are larger,the downstream recirculation effect caused by the swirling shear action is more significant,and the turbulent disturbance effect in the shear layer is stronger.In addition,due to the limited space between the adjacent swirls,the expansion effect of the downstream flame of the double swirls is weaker than that of the single swirl.The correlation analysis of scalar flux and gradient shows that the main reactants and products basically satisfy the gradient transport,and the gradient transport effect is more significant when the number of Kais large.However,for the intermediate products,the gradient diffusion hypothesis is not valid near the flame surface,which challenges the models based on the gradient diffusion hypothesis.
作者
肖华林
罗坤
王海鸥
金台
樊建人
XIAO Hualin;LUO Kun;WANG Haiou;JIN Tai;FAN Jianren(State Key Laboratory of Clean Energy Utilization,Zhejiang University,Hangzhou 310027,China;School of Aeronautics and Astronautics,Zhejiang University,Hangzhou 310027,China)
出处
《空气动力学学报》
CSCD
北大核心
2020年第3期611-618,共8页
Acta Aerodynamica Sinica
基金
国家自然科学基金重大研究计划(91741203)。
