【作者】 耿辉；

【导师】 周进；

【作者基本信息】 国防科学技术大学 ， 航空宇航科学与技术， 2007， 博士

【摘要】 本文利用流场显示技术和数值仿真,对超声速燃烧室中凹腔上游横向喷注燃料的流动、混合与燃烧特性进行了深入研究。论文分为三个部分:(1)平面激光诱导荧光(PLIF:Planar Laser-Induced Fluorescence)技术的基础研究与应用、(2)超声速燃烧室中横向喷注燃料的冷流研究、(3)超声速燃烧室中横向喷注燃料的反应流研究。在PLIF技术的基础研究与应用方面,详细推导了PLIF信号强度的数学表达式,给出了PLIF探测OH基浓度的方案以及PLIF探测丙酮浓度与流场密度的方案;通过设计PLIF测量系统中的控制时序,实现了在曝光门宽低于50ns的条件下对短脉宽PLIF信号的完整捕获;设计了高浓度丙酮蒸气加注系统,解决了在激发光能量较低的情况下丙酮PLIF信号的信噪比较低的问题。同时基于上述研究成果,应用丙酮PLIF技术对欠膨胀自由射流的密度场进行了显示与测量,取得了较好的效果。在超声速燃烧室中横向喷注燃料的冷流研究方面,以添加了丙酮蒸气的氦气模拟燃料,利用丙酮PLIF成像和数值仿真,研究了无凹腔燃烧室中壁面喷注燃料以及带凹腔燃烧室中凹腔上游喷注燃料的流动与混合特性,分析了喷注参数和凹腔结构参数的影响。研究发现:横向喷入的燃料在向来流方向急剧转向阶段,由于受大尺度运动和流向涡运动的强化,混合速率会大大提高。当增加燃料喷注流量时,采用提高喷注总压的手段较采用增大喷孔直径的手段更有利于增强扩散与混合。在凹腔上游横向喷注气态燃料时,燃料多分布于凹腔上方,少量会伴随凹腔剪切层的空间发展和湍流扩散而进入凹腔;提高喷注总压会减少进入凹腔的燃料质量;增大凹腔长深比有利于燃料进入凹腔,而增加凹腔深度或后壁倾角则相反;凹腔内部的低速流场有利于进入其中的燃料进行扩散和混合,能够扩大近壁面附近燃料的展向分布。在超声速燃烧室中横向喷注燃料的反应流研究方面,分别以氢气和乙炔作为燃料;利用OH基自发辐射成像、OH基PLIF成像以及数值仿真等手段,分别研究了凹腔上游喷注氢气燃烧的贫燃熄火当量比、火焰分布、火焰结构等特性,分析了喷注参数和凹腔结构参数的影响;利用高速摄影和CH基自发辐射成像等手段,分别研究了凹腔上游喷注乙炔的引导氢气点火过程、乙炔自燃点火过程以及乙炔燃烧反应区的火焰特性,分析了乙炔喷注位置和凹腔结构的影响。研究发现:在氢气喷口下游布置凹腔有利于氢气的自燃点火,加长凹腔时更有利于氢气自燃点火。在氢气喷注流量相同时,采用高总压喷注较采用低总压喷注更有利于自燃点火且燃烧效率更高。氢气燃烧火焰主要分布在凹腔上方或凹腔下游,火焰呈管状结构,管壁火焰包裹在氢气流的外围。增加氢气的当量比可使火焰区前移、火焰区范围和火焰强度增大。增大凹腔长深比或凹腔后壁倾角也可使火焰区前移、火焰强度增大。流经凹腔的新鲜混气和高温燃气进入凹腔,维持凹腔内部高温且富含活化分子的流场环境,而凹腔又通过传热传质不断向流经凹腔的新鲜混气供给热量和活化分子使其着火,从而形成了稳定的火焰。当利用引导氢气点燃乙炔时,点火时的火焰扩展平缓,改变凹腔结构或乙炔喷注位置对乙炔实现点火影响不大。壁面布置凹腔有利于乙炔自燃点火,乙炔发生自燃点火时火焰扩展迅速,改变凹腔结构或乙炔喷注位置对乙炔实现自燃点火影响很大;后壁较陡的凹腔有利于乙炔的自燃点火,乙炔在凹腔底壁前部横向喷注最易实现自燃点火,在凹腔上游或凹腔底壁中部横向喷注次之,在凹腔底壁后部横向喷注或在凹腔后壁逆向喷注均不易实现自燃点火。更多还原

【Abstract】 This research studies the flow, mixing and combustion properties of the transverse fuel injection upstream of the cavity in a supersonic combustor by means of experimental investigation and numerical simulation. The main contents of this research include three parts: (1) the fundamental research and application of planar laser-induced fluorescence (PLIF) technique, (2) the research of non-reacting properties of the transverse fuel injection in a supersonic combustor, (3) the research of reacting properties of the transverse fuel injection in a supersonic combustor.In the fundamental research and application of PLIF technique, the expression of PLIF intensity is deduced in detail and the detecting methods for hydroxyl radical (OH) concentration, acetone concentration and density of the flowfield are presented. By designing of the scheduling control system in the PLIF measurement system, we are able to obtain the short pulse width PLIF signal integrally at an exposure time less than 50ns. At the same time we designed the high concentration acetone vapor injection system to solve the problem of the signal-to-noise ratio of the acetone PLIF intensity being too low under the weak exciting laser. Based on these research results, we employed an acetone PLIF technique to visualize and measure the density flowfield of under-expanded free jet satisfactorily.In the research of non-reacting properties of the transverse fuel injection in a supersonic combustor, a helium jet adulterated with acetone vapor was employed to simulate a fuel jet. Using PLIF imaging of the acetone and numerical simulation, we researched the flow and mixing properties of the fuel injected from the wall in the non-cavity combustor and the fuel injected upstream of the cavity in the cavity-carrying combustor. And then the effects of the injection parameters and the cavity geometry parameters on these properties are analyzed.The research results show the mixing degree is enhanced by the large-scale movement and streamwise vortex movement when jets turn sharply toward the airstream, which increases the speed of the mixing of the fuel and the air remarkably. When the mass rate of the fuel is increased, diffusion and mixing can be enhanced more by increasing the injection stagnation pressure of the fuel than by increasing the diameter of the injection port. When the gaseous fuel is injected upstream of the cavity transversely, most of the fuel mass distributes above the cavity and a little fuel mass enters the cavity by going with the spatial evolution of the cavity shear layer and by the turbulent diffusion in the cavity shear layer. Increasing the injection stagnation pressure of the fuel will decrease the fuel mass entering the cavity. Increasing the length-to-depth ratio of the cavity is helpful in causing the fuel to enter the cavity. However, increasing the cavity depth or the aft ramp angle has opposite effects. The low speed flowfield in the cavity is helpful in making the fuel diffuse and mix and extending the spanwise distribution of the fuel near the wall.In the research of reacting properties of the transverse fuel injection in a supersonic combustor, hydrogen and acetylene were employed as the fuel. By means of spontaneous radiation imaging and PLIF imaging of OH and numerical simulation, the properties of lean blowout equivalence ratio, flame distribution and flame structure were researched. And then the effects of the injection parameters and the cavity geometry parameters on these properties are analyzed. By means of high speed photography and spontaneous radiation imaging of the hydrocarbon radical (CH), the ignition properties of the transverse injection of acetylene upstream of the cavity ignited by the pilot hydrogen flame and by its self-ignition and the flame properties of the combustion reaction area are studied. The influences of injection locations of the acetylene and the cavity geometry parameters on these properties are analyzed.The research results show that the cavity installed downstream of the hydrogen port is helpful in hydrogen’s self-igniting and lengthening the cavity helps even more. Under equal hydrogen mass rate, the injection under high stagnation pressure makes self-ignition easier and achieves higher combustion efficiency than injection under low stagnation pressure. Most of the hydrogen flame distributes above the cavity and downstream of the cavity. The flame structure is tubelike and the flame lying in the tube wall encloses the hydrogen jets. Increasing the equivalence ratio of the hydrogen causes the flame to move upstream and increase the flame area and the flame intensity. Increasing the length-to-depth ratio of the cavity or the cavity aft ramp angle causes the flame to move upstream and to increase its intensity. The unburned and mixed gas and the high temperature burning gas enter the cavity and keep the cavity flowfield at high temperature and abundant with active molecules. At the same time, the heat and active molecules are transferred continuously from the cavity to the unburned and mixed gas passing the cavity. And then the stable flame is formed. When the acetylene is ignited by the hydrogen pilot flame, the flame extends gently in the ignition process. At the same time, changing the cavity structures or the acetylene injection locations has little influence on the acetylene ignition properties under this condition. The cavity is helpful in self-igniting the acetylene. In the acetylene self-ignition process, the flame extends rapidly. Changing the cavity structures or the acetylene injection locations has great influence on the acetylene self-ignition properties. Increasing the cavity aft ramp angle makes the self-ignition of the acetylene to be easier. Transverse injection from the foreside of the cavity bottom wall is easiest to self-ignite, and transverse injection upstream the cavity or from the middle of the cavity bottom wall is second easiest, and transverse injection from the backside of the cavity bottom wall or reverse injection from the cavity back wall is not easy to self-ignite.更多还原