【作者】 孙晓晖；

【导师】 陈志华；

【作者基本信息】 南京理工大学 ， 力学， 2013， 博士

【摘要】 新型冲压推进系统,如超燃冲压发动机、斜爆轰波发动机与冲压加速器等,其流场结构非常复杂,且具有高瞬态特性。由于目前的相关研究还不充分,因而无法达到工程应用的要求,一系列问题尚需解决,如扩大可操控的飞行马赫数范围、强激波对推进系统进气道的影响等。另一方面,高速流场中,强激波与爆轰波导致研究对象周围的气流电离,使得应用磁流体(MHD)技术对强激波与爆轰波的控制和优化流场结构变成可能,相关研究仍处于初级阶段。本文基于带化学反应与MHD控制源项的Euler方程,分别采用混合Roe/HLL及WENO计算格式,利用自适应加密笛卡尔网格与沉浸边界法对新型冲压推进系统的波系结构及其MHD控制机理进行了研究。首先对管内爆轰波的诱导过程进行数值模拟,研究了爆轰波的诱导特性,验证了所采用数值方法的有效性,并揭示了弱激波绕射方块障碍物并在障碍物后方碰撞加速诱导爆轰波的机理。数值模拟了超燃冲压发动机双楔形进气道流场及其MHD控制过程,计算结果表明应用洛伦兹力可控制进气道上的斜激波,洛伦兹力的方向对MHD控制的效果具有重要影响,并且具有合适大小和方向的洛伦兹力可以同时将不同超声速来流情况下的斜激波恢复到设计情况,但其流场情况会稍有不同。通过对单、双楔斜爆轰波流场结构及其MHD控制过程的数值研究,表明,斜爆轰波可分为稳定与不稳定两种情况。对于稳定斜爆轰波,其波阵面位置基本固定,而不稳定斜爆轰波则相反。洛伦兹力可以将不同马赫数条件下的稳定斜爆轰波恢复到其设计位置,但是,对于双楔,布置在第一道斜劈表面的洛伦兹力无法有效控制第二道斜激波,当后楔倾角过大时,斜爆轰波流场将失稳。洛伦兹力可使不稳定斜爆轰波趋于稳定,却很难控制不稳定斜爆轰波恢复到设计位置,因此MHD控制的应用主要针对稳定斜爆轰波阵面。采用高精度WENO计算格式数值模拟了冲压加速器冷态实验。通过与相关实验结果对比,表明计算方法很好地描述了冲压加速器内部流场和激波结构,验证了WENO格式捕捉高速流场结构的有效性,并完整地呈现了弹丸周围激波的形成与发展过程及相关参数的变化情况,可以对冲压加速器冷态实验给予一定的指导与借鉴,并对接下来的热壅塞与超爆轰模态冲压加速器的研究提供指导。数值研究了热壅塞模态冲压加速器内的流场情况,研究了预混气体反应速率、弹丸形状与速度对冲压加速器工作状态与性能的影响。结果表明只有速度与反应速率相匹配,才能形成热壅塞模态流场,合理的弹丸形状可以使来流速度与预混气体反应速率相匹配的范围扩大。而且,当流场处于热壅塞模态,火焰阵面可以稳定在船型弹丸肩部后方,并产生最大推力；当火焰阵面稳定在弹丸底部时,推力受到尾涡脱落的影响产生脉动。进一步研究了超爆轰模态,冲压加速器内的流场情况,发现在一定的马赫数范围内,斜爆轰波可驻定在弹丸肩部或头部,且都能产生推力。对于典型的超爆轰模态(斜爆轰波驻定在弹肩),反应速率增加时,弹丸推力增大。对来流马赫数过低或过高的流场情况,采用洛伦兹力可扩大弹丸在典型超爆轰模态运行的马赫数范围,发现马赫数过低时,洛伦兹力可加速弹丸头部气流,使斜爆轰波驻定在弹肩,从而形成典型超爆轰模态。当马赫数为某定值时,若无洛伦兹力控制,则因涡的产生最终无法形成超爆轰模态,而洛伦兹力则可使斜爆轰波驻定在弹丸前楔,对弹丸产生推力,并使流场保持稳定。更多还原

【Abstract】 For the new types of ram propulsion systems, such as scramjet, oblique detonation wave engine and ram accelerator etc., their flow fields are very complex and have high transient features, the investigations of such fields are still inadequate to satisfy the practical requirement, a series of problems need to be solved, such as to expand their operation ranges to a wide range of Mach numbers and the infulences of high intensity shock waves influences etc. On the other hand, the strong shock waves or detonation waves of such propulsion systems can lead to a significant ionization of the air flow, which allows us to use the MHD (Magnetohydrodyamics) for the control and optimization of the flowfield. In this dissertation, based on the Euler equations with the chemical and MHD source terms, with the employ of the hybrid Roe/HLL scheme, Adaptive Mesh Refinement (AMR) Cartesian grid system and Immersed Boundary Method (IBM) to investigate the wave and flow structures of the new types of ram propulsion systems and their MHD control.Firstly, through the simulation of the detonation initiation accelerated by the collision of the diffraction shock waves, the numerical methods were verified, and our results revealed the mechanism that the wake shock waves diffract behind the square obstacles and collide to accelerate the induction of the detonation waves.The process of the MHD control of the double wedged inlet flowfield of a typical scramjet was also simulated. The numerical results show that, with the application of Lorentz force at the forebody of the first ramp, the lcoations of two oblique shock wave fronts at the inlet can be controlled, and the directions of the Lorentz force have significant effect on the MHD control process, moreover, the two oblique shock waves at off-design conditions can be restored to the desired location with proper magnitude and direction of Lorentz force, but the flowfield structures are slightly different from the desired case.The MHD control of the oblique detonation wave (ODW) induced by both single and double wedges has been investigated, the numerical results showed that MHD control can also return the location of a stable ODW front to its designed location. However, with the MHD control located on the surface of the first ramp, the second shock wave that generated at the corner of the double wedge could not be controlled. When the angle of the second ramp is large enough, the stable ODW becomes unstable and it cannot be manipulated with the MHD control. It is hard for the MHD control returning the unstable ODW front, but the front turns to be stable with proper MHD control. With the high order WENO scheme, we simulated the non-reactive flow field of a typical ram accelerator. The wake flow, including the shock wave structures, have been shown clearly, which agree well with corresponding experimental results. It is validated that WENO scheme is suitable for capturing the hypersonic flowfield and shock waves inside the ram accelerator. The generation and development of shock waves and relative parameters around the projectile have been presented, which can be used as a guide and reference for the cold launch experiments of ram accelerator.For the thermally choked ram accelerators, the influences of the gas reaction rate, the velocity and the projectile shapes on the states and performances of ram accelerator have been investigated numerically. It has been shown that the thermally choked mode occurs only when the variation of the reaction rate and velocity within certain limit, and a proper projectile shape can extend this limit. Furthermore, in a thermally choked mode, the flame front can be stable just behind the shoulder of a boat-shaped projectile, which generates the largest stable thrust. While the thrust generated with the flame stable at the projectile base vibrates due to the vortex shedding.Lastly, we investigated the flow field of the superdetonative mode of the ram accelerators, we found that with the increase of the velocity, there would be ODWs appeared at the shoulder and the head of the projectile, respectively, which can accelerate the projectile. For a typical superdetonative mode, the higher the reaction rate is, the larger its thrust becomes. The Lorentz force can extend the velocity area of the typical superdetonative mode from the cases that the velocity is too low or too high. As the velocity is too low, the Lorents force accelerates the flow of the projectile head, which makes the ODW staleb at the rear shoulder, however, for a certain incoming velocity, without the action of Lorentz force, the drag will be generated due to the appearance of vortexes, however, with the use of Lorentz force the stable ODW can be induced at the front wedge of projectile, and results to the generation of both thrust and stable flow.更多还原