【作者】 晏至辉；

【导师】 刘卫东；

【作者基本信息】 国防科学技术大学 ， 航空宇航科学与技术， 2013， 博士

【摘要】 本文以应用于双燃烧室冲压发动机的超声速混合层为研究对象，采用数值仿真与实验相结合的方法，对超声速混合层的流动、燃烧过程及其增强方法进行研究。为明确超声速混合层发展规律，利用混合LES/RANS方法计算隔板厚度、压力不匹配程度及燃料组分对超声速混合层发展的影响，并定量分析相应的混合效率和压力损失。发现一定范围内隔板厚度越大，混合越好，但总压损失也较大；燃烧流场的混合燃烧效果也随着隔板厚度增大而有所增加。冷流流场中，压力不匹配程度越高，混合相对较好，总压损失较小，但两者并非呈线性关系；燃烧流场的混合燃烧效率变化趋势与冷流流场基本一致。燃料中氢气浓度越靠近当量百分比，混合越好，但会增加总压损失。从被动混合增强和主动混合增强两方面对超声速混合层的混合增强进行了研究。发现随着凹腔长深比的增大，超声速混合层初始阶段涡的卷起提前，层流阶段距离缩短；涡结构呈现出较强的稳定性，涡耗散速率减慢。随着凹腔后缘倾角的增大，流场中下游段涡间距有减小趋势，涡结构呈现出较强的稳定性，涡耗散速率减慢。上下交错隔板构型的流向涡发展迅速，它的卷吸作用增大了空气和燃料接触面积，使燃料在很短的距离内实现了良好的混合；左右交错隔板构型流向涡的涡结构在距离隔板后缘40mm之前体现强的稳定性，在40mm-60mm的范围内涡结构迅速耗散。两种交错隔板对超声速混合层而言，都有混合增强效果，上下交错隔板增混效果要强于左右交错隔板。加入扰动的混合层涡结构尺寸明显大于没有扰动的情况，高频扰动的增混效果要强于低频情况。基于超声速混合层纹影图像分析不同构型隔板激波入射、反射位置和混合层增长速度、厚度和边缘结构等随时间震荡的特性。考察不同构型隔板混合层涡结构的卷起位置及涡运动速率。考察超声速混合层燃烧流场的着火过程中火焰的传播机制并描述了混合层中火焰的非定常特性。通过对比不同构型隔板混合层流场中OH基的分布，发现混合层中燃烧区域基本与混合层上下层气体掺混区域一致，其火焰基本形态由混合层的流动、混合特性主导；但混合增强方式对混合层燃烧流场的影响小于纯流动的情形。同时还发现，混合层上游燃烧的强度对混合层下游燃烧效果也存在一定的影响；混合层燃烧流场存在较强的三维特征，展向的扰动对混合层影响较大。更多还原

【Abstract】 The present research studied the flow/combustion mechanisms and theenhancement methods of the supersonic mixing layer, using different experimentalinvestigations and numerical simulation.In order to determine the discipline of the development of the supersonic mixinglayer, hybrid LES/RANS method is applied to simulate the influence of the clapboardthickness, the pressure-nonmatching degree and fuel species. The results suggest: withina certain range, the mixing efficiency，the total-pressure loss and the combustionefficiency grow with an increased clapboard thickness. In the nonreacting mixing layer,the higher the pressure-nonmatching degree is, the higher the mixing efficiency and thelower the total-pressure loss are; the pressure-nonmatching degree is nonlinear to themixing efficiency and the total-pressure loss. The trend of mixing and combustionefficiency in reacting mixing layer is consistent with no-reacting mixing layer. Themixing efficiency and the total-pressure loss increase when the reaction is getting closeto the chemical stoichiometry.Supersonic mixing layer is investigated by using passive and activemixing-enhancement methods. It is found that as the length-depth ratio of the cavityincreases,the vortexs in the mixing layer are rolled up at an earlier time,leading to ashorter distance during which the flow is laminar.Besides,the vortexs assume strongerstability and their dissipation rate decrease.As the aft-angle of the cavity increases,thespace between vortexs become shorter in the downstream regime of the flow field andthe vortexs also assume stronger stability and their dissipation rate decrease.Theup-and-down staggered clapboard makes the steamwise vortexs develop rapidly,theirentrainment increases the contact surface area between the fuel and the air,facilitatingmixing during a short distance.In the left-and-right staggered clapboard case,thestreamwise vortexs assume strong stability before a distance of40mm from theclapboard,while they are rapidly dissipated during a distance of40-60mm.Both of thetwo types of staggered clapboards have mixing-enhancement effect,with the formerbetter than the latter.The scales of vortexs with disturbance in the flow field areobviously larger than those without disturbance, and high-frequency disturbance assumebetter effect than that of low-frequency.Based on the schlieren photographs,with different clapboards, the unsteady featureof the incidence and reflection locations of the shock wave, the mixing layers’sincreasing thickness and boundary structures are investigated. The location wherevortexs are rolled up and vortexs’ moving speed are investigated. The flame propagatingmechanism during ignition period of the supersonic reacting mixing layer and theunsteadyness of the flame are investigated. By comparing OH radicals distribution under different clapboards cases, it is found that the combustion area basically is thesame as the mixing area, the flame structure is mainly influenced by flow and mixing.Besides, the effect of mixing-enhancement methods is suppressed more or lesscompared to the nonreacting case. The combustion intensity upstream does influencethat of the downstream and the flow field assumes three-dimensional feature, severelyinfluenced by spanwise disturbance.更多还原