准二维水下超声速垂直过膨胀射流研究

阐述了水下超声速气体垂直过膨胀射流的准二维实验研究和射流的数值计算结果。利用高速摄影仪在1000帧/s的拍摄速度下实时记录了过膨胀工况下水下垂直射流的喷射状态,清晰显示了水下气体垂直射流的演化过程;并利用专业软件FLUENT,对实验Laval喷嘴内外纯气相流场进行了数值计算,发现喷口附近存在复杂激波区,辅助分析了水下高速气体垂直射流的动态不稳定性形貌。实验与计算表明：在保持较小射流流量和保障较大马赫数的条件下,水下超声速垂直射流在水环境中引发的回击频率会得到减弱;准回击现象的发现证实了这一结论。这对于工程应用中的风口材料的＂空蚀效应＂的减弱提供了理论依据。     

激波冲击下Air/SF6斜界面不稳定性实验研究

激波在不同密度介质上的交互作用在可压缩湍流上具有重要的基础价值。激波在界面上的作用会引起Richtmyer-Meshkov不稳定性。激波不正规折射时,流场存在更多复杂的涡。研究马赫数为1.23、1.41的激波在初始倾角β=60°的Air/SF6界面上非正规折射的情况。入射激波的切向冲击和法向冲击的相互作用,在界面处产生涡,折射波在壁面发生马赫反射。利用阴影显示技术,给出了界面演化和混合的过程。     

真空导入模塑工艺树脂流动行为研究进展

综述了近年来真空导入模塑工艺树脂流动行为的研究进展,结合自己的研究成果系统地评述了真空导入模塑工艺中树脂的流动模型及机理、流动行为的数值模拟和流动行为的监测控制,并在此基础上对真空导入模塑工艺树脂流动行为的研究前景进行了展望。     

湍流、喷雾模型对氢氧火箭发动机燃烧仿真的影响

基于完善的压力隐式算子分裂(PISO)算法,通过改变κ-ε两方程湍流模型和喷雾模型,对氢氧火箭发动机不稳定燃烧进行数值仿真。比较理论分析和数值仿真的结果得出,在二维情况下,液滴碰撞模型和TAB液滴破碎模型不适于模拟氢氧火箭发动机不稳定燃烧;TVB液滴破碎模型与κ-ε两方程湍流模型的组合情况能够捕捉到燃烧室中的压力振荡,但不能体现出振荡频率;而采用Realizableκ-ε湍流模型不考虑液滴雾化模型时不但能够捕捉燃烧室内压力振荡情况,还能够很好地得出振荡频率的分布情况。     

氢喷射温度对氢氧火箭发动机燃烧稳定性的影响

应用CFD方法对氢氧火箭发动机中高频燃烧不稳定性进行了数值模拟,研究分析了不同工况条件下氢喷射温度对燃烧振荡的影响规律,得出了压力振荡频率变化规律及稳定性极限图。结果表明：在一定的氢喷射温度范围内会发生不稳定燃烧,且随着混合比的增大,发生不稳定燃烧的氢喷射温度上限增大;不稳定燃烧振荡主频呈倍频关系,且在氢喷射温度（70K～110K）内,振荡主频最大。     

Hydrodynamic instabilities and transverse waves in propagation mechanism of gaseous detonations

The present study examines the role of transverse waves and hydrodynamic instabilities mainly, Richtmyer–Meshkov instability (RMI) and Kelvin–Helmholtz instability (KHI) in detonation structure using two-dimensional high-resolution numerical simulations of Euler equations. To compare the numerical results with those of experiments, Navier–Stokes simulations are also performed by utilizing the effect of diffusion in highly irregular detonations. Results for both moderate and low activation energy mixtures reveal that upon collision of two triple points a pair of forward and backward facing jets is formed. As the jets spread, they undergo Richtmyer–Meshkov instability. The drastic growth of the forward jet found to have profound role in re-acceleration of the detonation wave at the end of a detonation cell cycle. For irregular detonations, the transverse waves found to have substantial role in propagation mechanism of such detonations. In regular detonations, the lead shock ignites all the gases passing through it, hence, the transverse waves and hydrodynamic instabilities do not play crucial role in propagation mechanism of such regular detonations. In comparison with previous numerical simulations present simulation using single-step kinetics shows a distinct keystone-shaped region at the end of the detonation cell.     

Heliopause stability revisited: dispersion analysis and numerical simulations

The heliopause, a surface separating the tenuous hot heliosheath flow and the dense, strongly magnetized interstellar flow, is subject to instabilities of the Rayleigh–Taylor and Kelvin–Helmholtz types. The dynamic evolution of this discontinuity is of considerable importance for understanding the neutral atom and cosmic-ray filtration at the interface. Here, we investigate the stability of the upwind heliopause in the presence of charge exchange collisions using both an analytic (dispersion relation) approach and a numerical model that includes the interstellar magnetic field. The linear analysis yields a cubic dispersion relation that admits imaginary solutions for the full range of wavenumbers, implying that the stagnation point on the heliopause is unconditionally Rayleigh–Taylor unstable to small perturbations propagating parallel to the discontinuity surface. We confirm this result by following the nonlinear development of the instability with a time-dependent simulation using a four fluid MHD-neutral numerical code. For the typical solar wind and LISM conditions, we obtain cyclical evolution of the upwind heliopause with a period of the order of 100 years. We also identify two areas of space physics where the instability may have important implications.     

A mesh optimization method using machine learning technique and variational mesh adaptation

Computational mesh is an important ingredient that affects the accuracy and efficiency of CFD numerical simulation. In light of the introduced large amount of computational costs for many adaptive mesh methods, moving mesh methods keep the number of nodes and topology of a mesh unchanged and do not increase CFD computational expense. As the state-of-the-art moving mesh method, the variational mesh adaptation approach has been introduced to CFD calculation. However, quickly estimating the flow fi...     

固冲发动机三维内流场数值计算与应用

利用三维隐式有限体积ＴＶＤ格式求解Ｎ－Ｓ／Ｅｕｌｅｒ方程组,数值模拟固体燃料冲压发动机（ＳＦＲＪ）突扩燃烧室、补燃室和喷管的统一内流场,研究了从亚声速到跨声速到超声速的整个工作过程,揭示了ＳＦＲＪ内复杂的流场结构,并与试验进行对比研究,数值结果与试验吻合很好。     

CCD互相关粒子图像测速及其在对抗流流场测量中的应用

在常规自相关粒子图像测速（ＰＩＶ）系统的基础上,发展了一个采用ＣＣＤ像机的互相关粒子图像测速系统。用这一新系统测量了对抗流流场的结果表明,这一技术克服了自相关粒子图像测速技术在测量具有滞止点的流场中的困难。实验说明,与自相关粒子图像测速技术相比,这一技术更快捷有效。