性能影响的数值研究

Numerical Investigation on Effects of Equivalence Ratio Distribution on Performance of Scramjet Combustor with Dual-Staged Injections

关键词:  当量比分配  双十字支板  部分预混火焰面模型  正癸烷

Key words:  Equivalence ratio distribution  Crossed dual-strut  Partial-premixed steady flame model  n-decane

摘要:

为了研究当量比分配对超燃燃烧室性能的影响，对煤油在基于双级支板喷注的双模态冲压发动机中的超声速燃烧过程进行了数值模拟研究。超燃燃烧室进口污染空气由烧氢补氧加热器提供，总温为1231K，入口马赫数为2.0。液态煤油通过两级十字型布置的支板直喷入燃烧室，全局当量比恒定为0.8，采用了三种不同的上下游燃料分配方案。数值模拟采用k-ω SST模型来模拟湍流；离散相模型来模拟煤油液雾的破碎、雾化、蒸发以及与连续场之间的耦合过程；部分预混火焰面模型来考察湍流与化学反应之间的相互作用；煤油采用正癸烷(C10H22)作为替代燃料，其半详细的化学反应动力学模型包括40组分141步基元反应。预测的三种工况条件下壁面静压分布均与试验值符合良好，表明本文采用的数值方法可以较为准确地描述大分子碳氢燃料的超声速燃烧过程。通过对燃烧流场的进一步分析，可以做出以下结论:燃烧室内存在着两个反应区，上游反应区前锋驻留在上级支板尾缘，下游反应区前锋驻留在下级支板尾缘。随着上游当量比从0.1提高到0.3，上游反应区逐渐从位于流道竖向中央的对称结构转变为向下底壁与侧壁交接的角区倾斜的非对称结构，下游反应区则逐渐缩小；预燃激波串起始位置向燃烧室进口移动，进入上游反应区的气流逐渐从超声速气流转换为亚声速气流，而进入下游反应区的气流逐渐从亚声速气流转换为超声速气流；燃烧室出口总压恢复系数从37.6%单调增加到41.1%，燃烧室内推力却从366.4N单调降低到331.8N；然而，燃烧室出口燃烧效率与上游当量比之间不存在单调相关性。

Abstract:

Numerical simulations were performed to investigate the effects of equivalence ratio distribution on the combustion performance of a liquid kerosene fueled dual-staged scramjet combustor. High enthalpy vitiated inflow at a total temperature of 1231K was supplied using a hydrogen-combustion heater. The Mach number at combustor inlet was 2.0. The fuel was injected into the combustor using crossed dual-strut. The global equivalence ratio was held constant to be 0.8，and three injection distribution schemes were conducted. The two-equation k-ω SST turbulence model was adopted to simulate the turbulence. The discrete phase model was utilized to predict the breakup，atomization，evaporation，and the coupling with the continuous phase of the liquid kerosene. The partial-premixed steady flame model was applied to consider the turbulence-combustion interaction. The n-decane was selected as the surrogate fuel of kerosene. Its skeletal mechanism included 40 species and 141 steps. The calculated wall pressure profiles in three fuel distribution schemes agreed well with the experimental values，illustrating that the present numerical method can provide a relatively accurate description of the supersonic combustion process of high molecular hydrocarbon fuels.Further analysis on the reacting flow field demonstrated that two reaction regions occurred in the combustor: the upstream reaction region was anchored at the trailing edge of the upstream strut，and the downstream one at the trailing edge of the downstream strut. With the upstream equivalence ratio increased from 0.1 to 0.3，the upstream reaction region was gradually transferred from its symmetric structure located in the vertical middle of the flow path to an asymmetric structure inclined towards the corner of the bottom and side walls; while the downstream one was contracted. The original location of the pre-combustion shock train propagated upstream. The flow entering into the upstream reaction region was gradually transferred from supersonic to subsonic，while that entering into the downstream reaction region from subsonic to supersonic. The exit total pressure recovery coefficient monotonically increased from 37.6% to 41.1%，while the net thrust was monotonically decreased from 366.4N to 331.8N. However，there was no monotonic correlation between the exit combustion efficiency with the upstream equivalence ratio.