激波管实验和果冻实验界面不稳定性数值计算

运用算子分裂技术,增加二阶空间中心差方法和两步Rung-Kutta时间推进方法计算动力学粘性以及热流部分对流场的影响,将可压缩多介质流体动力学高精度欧拉计算方法MFPPM发展到适用于NS(Nayier Stokes)方程的可压缩多介质粘性流体计算方法MVPPM.通过与界面不稳定性实验结果的比较,来检验计算方法的正确性,并验证计算程序的有效性.主要包括一个激波管实验和两个果冻实验,即英国AWE(Atomic Weapons Establishment)激波管实验和LLNL实验室的果冻环实验以及中国工程物理研究院流体物理研究所冲击波物理与爆轰物理实验室进行的爆轰驱动下单层果冻界面不稳定性实验.研究结果表明:数值模拟结果与实验测量结果以及对应时刻的实验图象均吻合较好.     

可压缩多介质粘性流体和湍流的大涡模拟

在可压缩多介质粘性流体动力学高精度计算方法MVPPM(multi-viscous-fluid piecewise parabolicmethod)基础上,引入Smagorinsky和Vreman亚格子湍流模型,采用大涡数值模拟方法求解可压缩粘性流体NS(Navier-Stokes)方程,给出适用于可压缩多介质流体界面不稳定性发展演化至湍流阶段的计算方法和二维计算程序MVFT(multi-viscosity-fluid and turbulence)。在2种亚格子湍流模型下计算了LANL(Los Ala-mos National Laboratory)激波管单气柱RM不稳定性实验,分析了气柱的形状、流场速度以及涡的特征,通过与LANL实验和计算结果的比较可知,Vreman模型略优于Smagorinsky模型,MVFT方法和计算程序可用于对界面不稳定性发展演化至湍流阶段的数值模拟。     

界面不稳定性引起混合过程的二维数值计算

在可压缩多介质流体动力学高精度欧拉计算方法多介质流体分段抛物方法(multi-fluid piecewise parabolic method, MFPPM)基础上,运用算子分裂技术,增加二阶空间中心差方法和两步Rung-Kutta时间推进方法计算动力学黏性以及热流部分对流场的影响,发展适用于NS(Navier-Stokes)方程的可压缩多介质黏性流体计算方法多介质黏性流体分段抛物方法(multi-viscousity-fluid piecewise parabolic method, MVPPM). 文中采用MVPPM对英国AWE(atomic weapons establishment)激波管实验进行二维计算,给出了与实验图像基本一致的计算结果;应用MFPPM和MVPPM分别对二维柱对称内爆动力学界面不稳定性及其后期混合过程进行数值模拟,给出内外界面演化、速度历史以及后期中心气穴不同半径内因RT(Rayleigh-Taylor)界面不稳定性引起的混合量分布情况,从计算结果比较可见黏性对物质界面处混合量的分布影响明显.      

柱形和球形壳体内爆界面不稳定性数值分析

为了更好地研究柱形和球形构型下果冻界面不稳定性发展,避免内爆聚心反弹前后直角坐标网格计算导致的误差,提高对流场和界面位置的计算精度,通过应用考虑了MVFT程序的网格适应性,使其能够适用于柱形网格和球形网格下的界面不稳定性数值模拟,特别是能够保证内爆聚心反弹前后流场和界面计算的稳定性。应用改进的计算程序对两种构型下的界面不稳定性进行了数值模拟,并对二者界面演化规律进行了详细讨论和归纳。结果表明:对于内外半径相同的柱形和球形果冻,聚心反弹时前者半径较小,而后者反弹时刻早于前者,其向内聚心和向外运动的速度最大值大于前者,对内部气体的压缩强度强于前者。对于外边界带有正弦扰动情况,除遵循上述规律外,计算还给出了峰谷转换现象。该项研究结果为进一步深入进行复杂构型下界面不稳定性高精度数值模拟研究提供了一种分析工具。     

超高速发射实验及其数值分析

采用多介质流体高精度欧拉并行计算程序HVL-MFPPM,对Sandia实验室和中国工程物理研究院流体物理研究所冲击波物理与爆轰物理实验室进行的两个超高速发射实验装置进行数值模拟,前者给出的二级飞片前界面速度历史与VISAR实验测试和HVL-CTH程序计算结果一致,后者给出二级飞片稳定时的速度和飞行姿态与实验测试结果吻合,同时还给出了128个和216个CPU计算的界面形状.为进一步获得更高二级飞片速度的实验装置设计提供了理论和数值分析基础.     

内爆压缩多层密绕螺线管的数值模拟

利用AUTODYN二次开发接口建立三维多层密绕螺线管数值模型,并实现周期性边界条件,应用光滑粒子动力学方法对内爆压缩多层密绕螺线管过程及其界面不稳定性开展数值模拟。计算结果表明,内爆压缩螺线管结构过程存在扰动快速增长至后期的界面失稳现象,与对应的实验结果较为相符。同时,计算显示螺线管结构参数对界面不稳定性发展具有显著影响,螺旋角度减小,结构压缩后期的界面不稳定性趋于严重;铜线直径减小,结构压缩后期的界面不稳定性趋于减弱。     

k-D-a-B 模型和 Richtmyer-Meshkov 不稳定性的数值模拟

给出一个适用于流体力学数值模拟的湍流混合模型。由于引入湍流质量通量和密度脉动关联量的演化方程，它比一般的ｋ－ε模型能更准确地描述界面不稳定性引起的可压缩湍流混合过程，并且可以不需要人为给定初始湍流场。我们用同一套参数模拟了不同Ａｔｗｏｏｄ数的激波管实验，数值结果与实验基本一致     

k-D-a-B 模型和 Richtmyer-Meshkov 不稳定性的数值模拟

给出一个适用于流体力学数值模拟的湍流混合模型。由于引入湍流质量通量和密度脉动关联量的演化方程，它比一般的ｋ－模型能更准确地描述界面不稳定性引起的可压缩湍流混合过程，并且可以不需要人为给定初始湍流场。我们用同一套参数模拟了不同Ａｔｗｏｏｄ数的激波管实验，数值结果与实验基本一致。     

气体动理学方法对斜界面不稳定性实验的数值模拟

介绍了基于BGK模型(Bhatnagar-Gross-Krook)的气体动理学数值方法(Gas Kinetic Scheme,GKS),通过计算多组分激波管问题对以GKS方法实现的MBCD程序进行了验证,表明了在接触间断处产生的震荡非常小,网格收敛性好。在多组分问题求解时各组分满足同温和同速的假设条件下,利用该程序开展了Air/SF6斜界面不稳定性实验的数值模拟,得出了不同时刻SF6的密度分布图,并得到交界面宽度、斜界面左右端相对位置在激波穿过斜界面后的变化情况。通过与实验结果的比较可知,GKS方法和程序在网格数为1024×200和512×100时得到的交界面宽度与实验值的最大误差分别为6.1%和7.3%,可用于对界面不稳定性问题的计算。     

可压缩多介质粘性流体的数值计算

将考虑热传导和粘性情况下的Navier Stokes方程描述的物理过程分解成3个子过程进行数值计算,即把整个流量计算分解成无粘性流量、粘性流量和热流量3部分,采用多介质流体高精度parabolic piecewise method（PPM）方法、二阶空间中心差方法和两步Rung-Kutta时间推进方法相结合进行数值计算。给出了激波管中Riemann问题和二维、三维Richtmyer-Meshkov界面不稳定性的Navier Stokes方程和Euler方程对比计算结果,显示了粘性对界面不稳定性的影响。     

一种杆式多爆炸成型侵彻体战斗部

为进一步提高周向多爆炸成型侵彻体战斗部的毁伤效能,设计了一种爆炸成型杆式侵彻体战斗部。结合数值模拟方法,对侵彻体的成型过程及飞散效果进行模拟,分析了外衬对侵彻体成型质量的影响,并设计出侵彻体结构密实的杆式MEFP战斗部。制备了有外衬和无外衬两种战斗部原理样机并进行静爆实验。实验结果表明,无外衬战斗部成型侵彻体对3 m处40 mm厚45钢板平均穿深为27 mm,有外衬战斗部成型侵彻体可贯穿3 m处40 mm厚45钢板;侵彻体对靶板的侵彻实验结果与模拟结果一致。通过设计外衬结构,战斗部成型侵彻体的成型质量和侵彻威力都大幅度提高。     

Verification of simulation for unwinding motion of cable in water by physical experiment

When a torpedo is launched from a mother ship, a fiber-optic cable that exchanges information between the torpedo and the mother ship is unwound from a spool so as to enhance the shoot-down performance. The unwinding motion of the fiber-optic cable has been numerically analyzed using steady- or transient-state equations of motion, but the simulation has not been verified by physical experiments. Therefore, in this study, the numerical results for the unwinding cable are verified with a lab-based physical experiment. The experiment considers realistic situations in which the cable is unwound from an outer spool package with three different unwinding velocities in water. The transient-state equation of motion is derived in a Cartesian coordinates system using Hamilton’s principle for an open system. In conclusion, the numerical results are similar to the motion of the unwinding cable in the physical experiment. Particularly, the numerical results indicate that the motion observed in the physical experiment coincides better with the simulation as the unwinding velocity decreases.     

Large Eddy Simulation of the Stable Boundary-Layer: A Retrospect to Nieuwstadt’s Early Work

Observations and theory presented in a paper by Nieuwstadt (J Atmos Sci 41:2202–2216, 1984) are reviewed and reconsidered. We have used a large eddy simulation (LES) model to make a 10-h rerun. Averaged results obtained for the last hour were considered to be representative for the wind-driven, quasi steady nocturnal boundary layer as reported in Nieuwstadt’s paper. The turbulence characteristics found with the LES model are in good to excellent agreement with the majority of the observations and confirms the uniqueness of the dataset, though the scatter in the data is (understandably) large. Laboratory experiments of the stable boundary layer might reduce the uncertainty in existing data and should be encouraged. The concept of local scaling, introduced by Nieuwstadt in 1984 was also confirmed by our simulations. Nieuwstadt’s experiment and local scaling theory of the SBL were a major achievement and an important contributions to our understanding of the SBL.     

Controlling the disturbances in a hypersonic flat-plate shock layer by unsteady action from the surface

The results of a wind-tunnel experiment on the joint action of periodic acoustic fast-mode disturbances of the outer flow and disturbances generated at the leading edge of a plate on the hypersonic (M_∞ = 21) viscous shock layer on the plate are presented. The possibility of positively controlling the intensity of density fluctuations in the plate shock layer by means of disturbances introduced from the leading edge is shown. Direct numerical simulation of the suppression (enhancement) of disturbances under the simultaneous action on the shock layer of the two-dimensional fast-mode acoustic waves in the outer flow and the source of two-dimensional suction/injection disturbances near the leading edge of the plate is performed under the experimental conditions. The experimental and calculated results are shown to be in good agreement.     

Conjugate heat transfer inside a porous channel

Analytical and numerical analyses have been performed for fully developed forced convection in a fluid-saturated porous medium channel bounded by two parallel plates. The channel walls are assumed to be finite in thickness. Conduction heat transfer inside the channel wall is also accounted and the full problem is treated as a conjugate heat transfer problem. The flow in the porous material is described by the Darcy–Brinkman momentum equation. The outer surfaces of the solid walls are treated as isothermal. A temperature dependent volumetric heat generation is considered inside the solid wall only. Analytical expressions for velocity, temperature, and Nusselt number are obtained after simplifying and solving the governing differential equations with reasonable approximations. Subsequent results obtained by numerical calculations show an excellent agreement with the analytical results.     

基于三路舵机驱动的扑翼飞行模型气动特性研究

扑动而形成非定常气动现象是扑翼飞行过程中产生高升力的主要原因。本文以Ellington实验的鹰蛾翅膀为原形,设计扑翼实验及数值计算模型。通过压差传感器对翅膀模型上翼面固定位置进行测压,分析前缘涡的产生及脱落情况(考虑动压效应)。测量上下翼面固定位置处的压差,揭示扑翼飞行中产生高升力的主要原因。利用烟风洞观察扑翼模型周围流场结构及特殊涡产生变化情况。另外,根据Ellington提供的升力关系式估算了扑翼模型在一个周期内的平均升力。最后,基于三维欧拉方程对扑翼飞行气动特性进行数值模拟,计算结果与实验吻合良好。     

内爆炸下钢管混凝土结构变形与破坏的试验分析及数值模拟

钢管混凝土结构由于具有良好的力学性能和低经济成本而受到广泛应用,因此对它的研究很多,但对它在爆炸作用下尤其是内爆炸作用下的研究很少,故分析钢管混凝土结构在内爆炸下的变形与破坏具有重要意义.本文通过试验与数值模拟方法,分析了内爆炸下钢管混凝土结构在具有二条预制狭缝时的变形与破坏情形.结果表明,钢管变形主要发生在靠近狭缝处,变形大小随药量的增加而增大,最终导致钢管在狭缝两端出现约45°方向的裂纹,引起钢管混凝土剪切破坏.     

环形浅池内硅熔体中的热流体波

为了了解工业Czochralski炉内硅熔体表面轮型的基本特征,对环形浅池内硅熔体的热毛细-浮力对流进行了三维数值模拟,硅熔池内径为15 mm,外径为50 mm,深度为3 mm,熔池外壁被加热,内壁被冷却,底部固壁和顶部自由表面均绝热或者允许一个垂直方向的传热。模拟结果表明,当径向温差较小时,熔池内会产生稳定的单胞热毛细-浮力流动,随着温差的增大,流动将转变为三维振荡流动,在熔体自由表面会出现沿周向运动的轮型,小的垂直方向的热流密度(3W/cm2)对这种振荡流动没有大的影响。同时,讨论了流动和温度波动的特征,并确定了振荡流动的临界条件。     

Direct numerical simulation of particle-laden plane turbulent wall jet and the influence of Stokes number

The distribution and motion of inertial particles in plane turbulent wall jet are investigated using direct numerical simulation, under the assumption of one-way coupling. To our knowledge, this appears to be the first direct numerical simulation of a particle-laden plane turbulent wall jet. It is shown that, in outer part of the wall jet, the behaviour of particles closely resembles that of a free plane jet. Due to the streamwise decay of particle Stokes number, the particle streaks formed in the near wall region of the wall jet are characterized by their intensity variation, which differs significantly from those in the channel flow. The streamwise growth of the particle velocity half-width is approximately equal to that of the fluid velocity half-width and the maximum velocity of particles decays slower than that of fluid due to inertia. The outer scaling can collapse the mean particle velocity in both the inner and outer region for heavier particles. In the buffer region, the particle–fluid velocity difference can be negative or positive depending on the Stokes number since there are two competing effects, namely the memory effect and turbophoresis. In the viscous region, the larger particles are on average faster than fluid and the velocity difference is found to be self-similar depending on outer Stokes number. The near-wall distribution of velocity difference is significantly correlated with the presence of high-momentum particles which are entrained by vortical structures generated in the outer region of the wall jet. These results are useful for environmental and engineering applications.