【作者】 韩省思；

【导师】 陈义良； 叶桃红；

【作者基本信息】 中国科学技术大学 ， 工程热物理， 2009， 博士

【摘要】 超声速燃烧冲压发动机(Scramjet)的研究近年来备受关注。由于实验方面投资较大以及测试手段的限制,数值模拟成为重要的研究工具。本文针对数值模拟中湍流模型这一重要因素进行研究,主要做了以下几个方面的工作:发展了四个具有更高计算精度的广义可压缩性修正k-ε湍流模型;研究并发展了联合RANS/LES方法用来模拟非稳态湍流流动;对多种复杂的超声速流动、超声速燃烧问题进行了深入研究;提出了利用分流技术强化超声速燃烧的技术。以往RANS湍流模型可压缩性修正研究集中在膨胀可压缩性修正的模化这一部分。在国外基础研究方面取得的最新初步研究成果基础上,本文引进并发展了其它部分的广义上的可压缩性修正,即结构可压缩性修正及激波不稳定性修正。在标准k-ε湍流模型基础上,耦合以往的膨胀可压缩性修正,发展了四个广义可压缩性修正的k-ε湍流模型。以可压缩混合层为基础,前两个模型中发展了结构可压缩性修正模型,用来抑制过大的湍流动能增长,能够很好地预测到混合层受抑制的发展趋势。后两个修正模型除了耦合研究已经较成熟的膨胀可压缩性模型,又从另外的角度出发,发展了激波不稳定性修正模型,用来抑制激波区域内过大的湍流动能产生。由于后面这两个修正模型综合考虑了自由发展的混合层中的可压缩性效应以及强间断激波的不稳定性脉动两部分效应,计算精度得到了进一步提高,尤其是显著提高了对高速流动中流体分离现象的模拟精度。结果初步表明,其中一个修正模型对流体分离的预测优于工程中广泛使用的k-ωSST湍流模型。联合RANS/LES方法既能保证明显改善RANS方法的计算精度,又能明显降低LES方法的计算量,是很有潜力的一种方法。针对由模型参数控制计算分区的这一类RANS/LES方法,本文研究了多种不同形式的联合方法。理论上推导出参考长度尺度为湍流积分长度尺度的联合方法本质上是一致的,与LES方法中应用很广的Smagorinsky亚网格尺度模型本质上相同。而以Kolmogorov长度尺度为参考尺度的联合方法,依据计算条件不同,可从RANS模拟直接过渡到DNS模拟。提出了一个采用指数形式构造的联合RANS/LES方法。应用联合RANS/LES方法研究了经典的方柱绕流流动以及超声速混合层流动。对发展的四个可压缩性修正的k-ε湍流模型进行了验证,并应用这些模型研究了一些复杂的超声速流动、燃烧现象。计算了超声速混合层、超声速后台阶、跨声速凸包流动、超声速横侧射流等复杂流动,以及超声速受壁面限制混合层燃烧、超声速横侧射流燃烧等工况。验证了四个修正模型的计算精度并对比分析了四个修正模型的优缺点。研究了可压缩性(包括膨胀可压缩性、结构可压缩性以及激波不稳定性)对混合层发展的抑制和对流体分离的强化,以及这些效应在燃烧工况下对超声速燃烧特性的影响。壁面入射是燃料进入超声速燃烧室最基本的一种入射方式。研究了这种方式下形成的超声速横侧射流流场。根据流场特性,提出了利用分流强化超声速燃烧的技术,即利用一个通道连通燃料入射孔的上下游,将上游高压流体部分分流到下游低压区,通过改变流场结构,达到强化燃烧的目的。研究内流及外流两种情况下,燃料具有不同入射压力时分流强化超声速燃烧的规律及机理。更多还原

【Abstract】 The research on Supersonic Combustion Ramjet(Scramjet) has been widely concerned in recent years.As the vast investment requirement of experimental research as well as the restrictions on the measuring and testing technique,numerical simulation method has become an important research tool. In this paper,turbulence modeling,one of the key issues in numerical simulations,has been deeply studied.The major research works and progresses are:developed several compressibility modification RANS turbulence models with a higher simulation accuracy;research and development of hybrid RANS/LES model to simulate complex unsteady turbulent flows;deeply research on a variety of complex supersonic flows and supersonic combustion problems relevant;proposed a technology to enhance supersonic combustion utilizing shunting.Traditional compressibility modification for RANS turbulence models generally focus on the dilatational compressibility modifications.Based on the latest primary research findings abroad,other parts of the generalized compressibility modifications were introduced and developed,viz.structure compressibility modification and shock unsteadiness modification.In the framework of standard k-εturbulence model,four generalized compressibility modified k-εturbulence models were proposed coupling with the traditional dilatational compressibility modifications.On the basis of compressible mixing layers,structure compressibility modeling was developed in the two first models.It can depress the overlarge turbulent kinetic energy,and can predict the depressed spreading rate of mixing layers very well.From a different point of view,shock unsteadiness modeling was developed in the other two models coupled with well developed dilatational compressibility models.The excessively production of turbulent kinetic energy can be depressed in the shock regions.As these two factors were considered together in the later two models,viz.the compressibility effect in free developed mixing layers and the unsteadiness effect of strong shocks,the numerical accuracies were further improved,especially for the prediction of fluid flow separation in high speed flows.Primary results show that one of them performs better than the widely used k-ωSST model in engineering applications for the flow separation prediction.The hybrid RANS/LES method demonstrates advantages in more accurate predictions than RANS method and much fewer computation costs than LES,and thus a very potential methodology.Focus on the kind of hybrid method in which the zonal computations are controlled by the model parameters, various hybrid methods were studied with different form.The theoretical deduction shows that these models utilizing the turbulence integral length scale as the reference length scale are essentially the same,and is also the same with the most popular Smagorinsky Subgird-Scale model in LES.But those utilizing the Kolmogorov length scale as reference length scale,can evolve from the RANS calculation directly to DNS simulation dependent on the simulation conditions.A new hybrid method was proposed applying an exponential form.The classic bluff body stabilized flows and supersonic mixing layers flows were studied accordingly.The four modified k-εturbulence models were evaluated,and applied in the studies on complex supersonic flows and supersonic combustion problems.The supersonic flow cases are supersonic mixing layers,the supersonic backward facing flows,the transonic flow over an arc bump,supersonic flow interacted with transverse injection etc.The supersonic combustion problems concerned here are supersonic wall-bounded reactive mixing layers,supersonic combustion with transverse fuel injection etc.The four modified models were validated and compared.The compressibility effects(including the dilatational compressibility,structure compressibility and shock unsteadiness effect) were studied on the depression of the mixing layers and enhancement of fluid flow separation,and these effects on the supersonic combustion performance were also investigated.The wall injector is the most basic fuel injector in supersonic combustor.The relevant flow field was studied.Based on the flow structure,a supersonic combustion enhancement technology was proposed utilizing shunting that is to connect the upstream region and the downstream region of fuel injection slot through a channel.Higher pressure fluid upstream partly shunts into downstream region and the flow field was changed correspondingly,hence the combustion was enhanced.The mechanics and discipline of shunting effects on combustion enhancement were investigated under different injection pressures both in the external and internal supersonic flows.更多还原