【作者】 夏强；

【导师】 武晓松；

【作者基本信息】 南京理工大学 ， 航空宇航推进理论与工程， 2011， 博士

【摘要】 近年来,固体燃料冲压发动机备受世界各国关注,与其它发动机相比,固体燃料冲压发动机具有比冲高、结构简单等特点,在超声速导弹和增程炮弹方面具有广阔应用前景。本文以小口径固体燃料冲压发动机增程炮弹为应用背景,以计算流体动力学软件FLUENT为工具,结合理论分析、数值模拟和实验等手段,对固体燃料冲压发动机的燃烧和内流场特性及其影响因素进行了深入系统地研究,为固体燃料冲压发动机的研制奠定理论和实验基础。本文主要工作如下：一、利用二维轴对称N-S方程对唇口前缘钝化的小口径超声速弹用进气道内外复杂流场进行了数值模拟,湍流模型为RNGk-ε两方程模型,数值格式为一阶迎风格式。所得流场结构清晰,获得了在设计马赫数下不同外罩唇口前缘钝化半径对进气性能参数的影响。结果表明：在唇口前缘钝化半径合理(r/H=1.3%)的情况下,进气道的稳定工作范围变宽,总压恢复系数提高,唯一不利因素为进气道总阻力有所增大。然而,当唇口前缘钝化半径过大(r/H=2%)时,钝化唇口前缘处产生的低速区使附面层变得很厚,对进气道内流场结构造成严重影响,进气道的稳定工作范围迅速变窄。二、利用三维雷诺平均N—S方程,在不同攻角和来流马赫数条件下,对带侧向支柱的某小口径固体燃料冲压增程弹用混压式进气道的内外复杂流场进行了数值模拟,并完成了风洞实验,得到了不同状态下进气道的纹影图片、沿程静压分布及进气道出口总压变化规律。数值模拟所得流场结构与风洞实验纹影图一致,所测静压与总压数据和计算值吻合良好,从而验证了数值模拟的可靠性。结果表明,所设计的弹用超声速轴对称混压式进气道在设计状态(Ma=3)和非设计状态(Ma=2.5)均能有效工作,并且在α=0°～6°的范围内具有良好的攻角特性。进气道出口马赫数约为0.3～0.4,能够满足小口径固体燃料冲压发动机燃烧室对入口马赫数的要求。三、利用Rihani-Doraiswamy和Benson两种基团贡献法,估算出了单体MMA(C5H8O2)的定压比热、标准生成焓和熵值等热力学数据。根据推进剂分解原理,结合计算流体动力学软件FLUENT的用户自定义函数进行二次开发,并采用两步化学反应模型、RSM模型、涡耗散湍流燃烧模型和一阶迎风格式,建立了PMMA在固体燃料冲压发动机燃烧室内的燃烧模型。对不同来流空气质量流率、来流空气总温、药柱通道直径等工况,进行了PMMA在固体燃料冲压发动机内燃烧的数值模拟研究,得到了燃烧室内的流场结构、温度及组分分布。结果表明,随着轴向位置的增大,燃料局部退移速率先增大后减小。增大入口空气温度和质量流率均使平均退移速率近似按指数关系增大,燃烧室温度亦随之增大。增大入口药柱通道直径使得再附点后移,而平均退移速率则近似呈指数关系减小四、设计了固体燃料冲压发动机直连式实验发动机,采用镁/聚四氟乙烯为点火药,在国内首次完成了以PMMA为燃料的固体燃料冲压发动机直连式实验,采用电磁阀和数显时间继电器精确控制实验时间,发动机点火可靠,工作稳定。对不同药柱通道直径、来流空气质量流率和出口喷管等工况进行了实验研究。实验结果表明,当药柱通道直径(Dp=30mm)较小时,固体燃料冲压发动机燃烧室产生类似于固体火箭发动机内的侵蚀效应。燃烧室压强越低,燃料平均退移速率、补燃室温度均随之降低,然而这种影响在低压(<O.8MPa)条件下是有限的；此外,增大药柱通道直径,使得总燃烧面积增大,尽管燃料平均退移速率有所降低,但是总燃气质量流率仍然增大,从而提高补燃室压强和温度。点火药量和能量以及点火药燃烧的持续时间均是点火能否成功的控制因素。对于给定的点火药品种,在点火药药量一定的条件下,增大来流空气质量流率和降低来流总温对点火都是不利的。实现成功点火的可行方法是增大点火药药量。数值模拟值与实验结果较为吻合,平均燃料退移速率最大误差约为7.7%；补燃室压强最大误差约为15.3%；补燃室温度最大误差约为22%。更多还原

【Abstract】 In recent years, solid fuel ramjet (SFRJ) has become a very attractive propulsion system for many researchers due to its high special impulse and simple structure compared to other air breathing engines, which has a wide application prospect on supersonic missile and extended-range projectile.The schematic design and performance analysis evaluation method, combustion and internal flow field characteristics and their relative conditions of Minor-diameter SFRJ extended-range projectile were studied detailedly and comprehensively by means of theoretical analysis, experimental investigation and numerical simulation, and the computational fluid dynamics software FLUENT was used as a tool. It has laid a foundation of theory and experiment for the SFRJ. In this paper, the work reads as follows:(1) The complex flow field of a minor-diameter supersonic mixed-compression ramjet inlet with blunted-lip cowl was numerically simulated by using the 2D-axisymmetric N-S equations, and the flow structures were clearly obtained. The two-equation RNG k-e turbulence model and the first order upwind scheme were used. The influence of different bluntness radius of cowl lips on the performance parameters of the inlet at design Mach number was studied. The results show that:the reasonable increase of bluntness radius of the cowl lip induces the stable operation range of inlet broadens, the total pressure recovery increases, and the only disadvantage was the increase of total drag of inlet. However, when the bluntness radius of cowl lip was too bigger(r/H=2%), the low speed area around the blunted-lip cowl makes the boundary layer become thicker. Consequently, the interior flow field of inlet was destroyed, and the stable operation range of inlet becomes narrower rapidly.(2) Under the condition of different angles of attack and inflow Mach numbers, the complex flow field of a mixed-compression inlet of minor-diameter SFRJ extended-range projectile with struts was numerically simulated by using the 3D Reynolds-averaged N-S equations, and also wind tunnel test has been achieved. The schlieren photographs of inlet and the distribution of static pressure along the inlet and the influence of different operations on total pressure at the exit of inlet were obtained. The results indicate that numerical flow structure and wind tunnel test schlieren photographs of inlet were identical. The experimental data, such as static pressure and total pressure, were in good agreement with the numerical results, and the reliabilities of the numerical simulation methods in this paper were verified.The results show that:under the the design(Ma=3) and off-design condition (Ma=2.5), the designed mixed-compression supersonic inlet both work effectively, and also has favorable angles of attack characteristic inα=0°～6°range. The Mach number of exit plane was about 0.3～0.4, which can satisfy the requirement of solid fuel ramjet combuston chamber on the Mach number of combustion chamber inlet.(3) Compared with Rihani-Doraiswamy and Benson group contribution method, the thermodynamics data of methyl methacrylate(C5H8O2) were estimated, such as special heat at constant pressure, standard enthalpy of formation and entropy. According to pyrolysis principle of propellant, based on secondary development technology by using the User Defined Functions, which was included in software FLUENT, the combustion model of (Polymethylmethacrylate) PMMA in SFRJ combustion chamber was established. Its combustion flow was described with two-step chemical reaction model, RSM turbulent model, Eddy Dissipation turbulent combustion model and first order upwind scheme, then the flow field structure, temperature and species distribution in SFRJ combustion chamber also were analyzed. Based on above, the flow field of SFRJ combustor chamber was numerically simulated, and the fuel was PMMA. It was analyzed the influence of the parameters, such as fuel port diameter, air total temperature, air mass flow rate etc.then. The flow field structure, temperature and species distribution in SFRJ combustion chamber also were obtained.The results show that:as the axial distance increases, the local regression rate increases at first then decreases gradually. In addition, the increase of inlet air temperature and mass flow rate both induces the mean regression rate of PMMA approximately exponential increase, and the combustion chamber temperature also increase.As the fuel port diameter increases, the reattactment point moves downstream, and the mean regression rate of PMMA approximately exponential decrease.(4) The SFRJ direct tube test motor was established. For the first time in domestic, the combustion behavior of PMMA in SFRJ was performed using a direct tube test facility, and the amorce was Mg/PTFE. In order to control the test time accurately, the electromagnetic value and digital display time relay were used.The experiments results prove that the ignition method was reliable, and the motor works stably. The effects of factors, such as air mass flow rate, air total temperature and fuel port diameter on regression rate and performance was investigated experimentally. The results show that:While the fuel port diameter was smaller (Dp=30mm), the SFRJ combustion chamber will produce phenomenon similar to erosion effect in solid rocket motor. As the combustion chamber pressure decreases, the fuel mean regression rate and aft -mixing combustion chamber temperature both decreases. However, at the condition of low pressure (0.8MPa), this effect was limited. In addition, the increase of fuel port diameter induces the total fuel combustion area increases. Although the fuel mean regression rate decreases, the total fuel mass flow rate still increases. Therefore, the aft-mixing combustion chamber pressure and temperature both enhances. For a given amorce, the mass and energy of amorce as well as combustion duration of amorce were governing factors of the success of ignition. When the amorce mass was a certain quality, increases the air mass flow rate and decreases the air total temperature both will have negative effect on the ignition process. In order to achieve ignition process successfully, increases the aomrce mass was the feasible method.The predicted results of the numerical model coincide well with the experimental data, the reliability of numerical model was verified. The error of mean regression rate was less than 7.7%, the error of pressure of aft-mixing combustion chamber was less than 15.3%, the error of temperature of aft-mixing combustion chamber was less than 22%.更多还原