弹道枪不同水深下全淹没式发射膛口流场的数值分析

为了解弹道枪水下全淹没发射时,水深对膛口流场演化特性的影响,建立了二维轴对称非稳态膛口流场模型。采用流体体积函数多相流模型、标准k-ε湍流模型和Schnerr-Sauer空化模型,结合动网格及用户自定义函数技术,对水下全淹没发射膛口流场演变全过程进行了数值模拟。搭建了弹道枪水下可视化射击实验平台,对12.7 mm口径弹道枪在水中全淹没式发射时膛口流场演化过程进行了观测,并验证了数值模型的合理性。在此基础上,对比了不同水深下（h=1～100 m）膛口流场的演化特性。通过对比发现：在不同水深条件下,在膛口流场影响范围内,弹丸膛外行程随时间的变化均满足指数函数规律;水越深,膛口流场典型波系结构形成所需时间越长,且燃气在膛口轴向马赫盘处的温度和压力峰值越低,压力振荡幅度也越小,更快趋于平稳,但在径向上,水越深,压力振荡持续时间越长。

     

膛口流场的数值模拟

本文使用严格二维的FCT算法数值模拟美国M16 5.36毫米自动步枪的非定常的轴对称膛口流场。用此方法不仅可得到膛口冲击波的发展过程,而且可得到不少数值方法不易得到的马赫盘的发展过程。本文计算结果与Schmidt的实验结果作了比较,二者吻合较好。这一结果为进一步开展更复杂(考虑弹丸、膛口制退器等)的膛口流场的数值模拟奠定了基础。     

膛口流场一维简化非傅里叶传热模型

针对膛口流场复杂的传热现象提出一个简化的工程计算模型。根据该模型得出:在一定条件下，流场内存在非线性波传热模式，并把运动的膛口焰火球近似看成一个非线性波，所得计算结果与实验数据相符。     

膛口反应流并行数值模拟

采用轴对称多组分N-S方程对含有高速运动弹丸的膛口反应流进行了数值模拟.控制方程采用时间分裂方法并在大型计算机上采用MPI方法进行多核并行求解,其中对流项采用二阶AUSM+格式和MUSCL插值方法进行处理,燃气采用氢气-空气混合气,反应机理为9组分19步基元反应.对于弹丸引起的网格运动,采用嵌套网格法处理.并行验证算例与串行计算结果一致,采用20个CPU计算时效率为64％.根据数值结果详细讨论了发射过程中的气体动力学和化学动力学过程,并且通过对两种条件下的计算结果比较分析了化学反应对膛口流场发展的影响.结果表明,上述算法能够较为正确地模拟弹丸和化学反应对膛口流场的影响,并大大提高了计算速度.     

含化学反应膛口流场的无网格数值模拟

基于无网格方法,对包含大位移运动边界和非平衡化学反应的膛口流场进行了数值模拟。所发展算法是基于线性基函数最小二乘显式无网格方法,忽略黏性及湍流的影响,对流场采用ALE(arbitrary Lagrangian-Eulerian)形式的Euler方程描述,对流通量和化学反应源项采用多组分HLLC(Harten-Lax-van Leer-Contact)格式和有限速率反应模型计算,对于运动边界造成的点云畸形采用局部点云重构方法处理,重构过程中采用虚拟边阵面推进。对圆柱绕流和激波诱导燃烧流场进行了数值模拟,验证了重构方法和化学反应计算的有效性。最后对12.7 mm口径机枪膛口流场进行了模拟,结果同实验照片、非结构网格方法结果吻合较好,数值结果清晰地再现了膛口初始冲击波、膛口冲击波、欠膨胀射流波系结构的动力学发展过程,以及膛口焰的时间、空间分布特征。

     

基于ALE方程的动网格膛口流场数值研究

基于ALE(Arbitrary Lagrangian-Eulerian Equation)方程的有限体积法,采用高精度Roe方法及结构化动网格,利用嵌入网格技术及动边界条件,对弹丸由膛内高压气体推动射出到完全飞高初始流场的整个过程进行了数值模拟.根据数值结果绘制了膛口流场密度和压力分布的时序图,形象地再现了膛口流场中初始激波、弓形激波及膛口冲击波,以及接触闻断、漩涡和剪切层等的动力学发展过程.结果基本反映了膛口流场的典型变化特征,为进一步研究真实膛口流场(如带化学反应、湍流等)奠定了基础.     

含内插管扩张型抑制装置的膛口流场数值研究

采用ＴＶＤ格式求解Ｎ－Ｓ方程，数值模拟了含内插管扩张型抑制装置的膛口流场，展示了由膛口冲击波包围着的特征多变的射流结构的演变过程，模拟结果与实验照片相符。分析了膛口冲击波与射流结构的相互作用，揭示了锥状冲击波和锥状燃气团的形成机理。     

小口径膛口射流噪声的数值模拟

为了研究小口径武器的膛口气动噪声特性,采用CFD-CAA耦合算法对7.62 mm枪的射流噪声场进行了数值模拟。由于膛口流场结构复杂,在目前的计算发展水平下还不足以采用CAA直接法,因而本文中采用混合方法,即首先采用CFD方法计算7.62 mm枪的膛口流场,然后利用所得结果,采用声学方程计算射流噪声,具体为膛口近场采用LES进行计算,远场声场采用FW-H声拟法计算。通过对比验证实验,验证了该计算方法的可行性。然后,对7.62 mm枪射流噪声进行了数值模拟,分析了噪声指向性,绘制了声压级云图。研究表明：在本文的计算条件下,射流噪声强度主要集中在近膛口区域;且射流最大噪声主要分布在与轴线方向成30°~60°范围内。

     

带制退器的膛口射流噪声数值模拟与实验研究

为了研究膛口装置对膛口噪声气动特性的影响,对带膛口制退器的某小口径武器的膛口射流噪声进行了数值模拟和实验研究。采用计算流体力学CFD (computational fluid dynamics)-计算气动声学CAA (computational aeroacoustics)耦合算法对膛口噪声进行数值模拟,即对膛口流场进行瞬态CFD模拟,获取流场数据,然后利用所得到的结果采用声学方程模拟声源信息求解声场。基于数值模拟结果,分析了膛口流场变化及噪声的指向性分布,并与实验结果进行了对比。研究表明：膛口制退器的安装改变了膛口流场结构,影响了膛口射流噪声的指向性分布。计算结果与实验结果的误差小于9%,验证了该计算方法的可行性。研究结果可为膛口射流噪声的预测及膛口制退器的设计提供一定的参考。

     

叠层板状元件在流场中固有振动特性分析

本文对核反应堆中叠层板状元件的干、湿模态固有频率与振型进行了理论分析和数值计算,提出了将该结构视为多层平行板梁与整体单梁的对接问题的动力特性分析方法,计算与实测结果吻合较好．     

Flow field and thermal characteristics in a model of a tangentially fired furnace under different conditions of burner tripping

Tangentially fired furnaces are vortex-combustion units and are widely used in steam generators of industrial plants. The present study provides a numerical investigation of the problem of turbulent reacting flows in a model furnace of a tangentially fired boiler. The importance of this problem is mainly due to its relation to large boiler furnaces used in thermal power plants. In the present work, calculation of the flow field, temperature and species concentration-contour maps in a tangentially-fired model furnace are provided. The safety of these furnaces requires that the burner be tripped (its fuel is cut off) if the flame is extinguished. Therefore, the present work provides an investigation of the influence of number of tripped burners on the characteristics of the flow and thermal fields. The details of the flow, thermal and combustion fields are obtained from the solution of the conservation equations of mass, momentum and energy and transport equations for scalar variables in addition to the equations of the turbulence model. Available experimental measurements were used for validating the calculation procedure. The results show that the vortex created due to pressure gradient at the furnace center only influenced by tripping at least two burners. However, the temperature distributions are significantly distorted by tripping any of the burners. Regions of very high temperature close to the furnace walls appear as a result of tripping the fuel in one or two of the burners. Calculated heat flux along the furnace walls are presented.     

Numerical investigations on dynamic process of muzzle flow

The integrative process of a quiescent projectile accelerated by high-pressure gas to shoot out at a supersonic speed and beyond the range of a precursor flow field was simulated numerically. The calculation was based on ALE equations and a second-order precision Roe method that adopted chimera grids and a dynamic mesh. From the predicted results, the coupling and interaction among the precursor flow field, propellant gas flow field and high-speed projectile were discussed in detail. The shock-vortex interaction, shockwave reflection, shock-projectile interaction with shock diffraction, and shock focus were clearly demonstrated to explain the effect on the acceleration of the projectile.     

固体差动随行装药高初速火炮内弹道理论分析

提出了一种基于差动原理的固体差动随行装药的高初速火炮发射方案,该方案能有效克服传统随行装药技术提高初速必将伴随射弹底部最大压力增加的缺点。它的主要特点是运用差动原理,实现不同组合件之间的速度不同,自动压缩储能室使随行工质向弹后连续喷射,有效抑制和消除了弹丸运动引发的稀疏波影响,提高了火炮工作容积利用率。推导了差动随行组合弹丸不同组合件动力学模型,给出了弹载工质物理量分布关系式。计算结果表明,在最大膛压、飞行弹丸底部最大压力、弹重及弹丸行程等不变条件下,随行药量取10.2 kg,某大口径火炮的弹丸初速可提高26%,火炮工作容积利用率提高约44%。该方案可为火炮提高初速和实现超远程发射提供新的途径。     

Flow field characteristics of an axisymmetric sudden-expansion pipe flow with different initial swirl distribution

The results of an experimental investigation depicting the effects of swirl profile on confined flows in a sudden-expansion coaxial dump combustor are presented. Three swirlers (free vortex, forced vortex, and constant angle) with the same nominal swirl number were designed and fabricated to study the effects of swirl type on the isothermal dump combustor flow field. Imparting swirl to the inlet flow resulted in a considerable reduction of the corner recirculation length, a marked increase in turbulent mixing activity, and in one case creation of a central recirculation zone. This article highlights the importance of the combustor inlet swirl profile and shows that swirl type as well as swirl strength can affect the flow field significantly. The present database is well suited for numerical codes development and validation.     

Numerical investigation on dynamic characteristics of flow field in cyclone separators with different dust hopper structures

The dynamic characteristics of flow field in cyclone separators with different dust hopper structures were studied by coupling Reynolds Stress Model (RSM) and Lagrangian Particle Tracking (LPT) methods. The characteristic frequencies of cylinder section, cone section and dust hopper were calculated as f₁ = 53 Hz, f₂ = 65 Hz, and f₃ = 8 Hz by using Fast Fourier Transform (FFT) method, respectively. Based on the effects of f₃ on the motion of vortex, the separated space was divided into none affected region, weakly affected region, and strongly affected region. The characteristic frequency of dust hopper increased with the decrease of dust hopper diameter, while it was independent of the height. The dust hopper with d = 1.5D (model D3) and h = 1.5D (model H3) can significantly decrease the effect of back-mixing on the motion of inner vortex, which is beneficial to improve the efficiency of cyclone separator.     

燃烧轻气炮多级渐扩型燃烧室流场特性数值研究

为了分析多级渐扩型燃烧室结构对燃烧轻气炮氢氧燃烧特性的影响, 通过计算流体力学方法, 分别对采用传统圆柱型燃烧室和多级渐扩型燃烧室的燃烧轻气炮氢氧燃烧发射过程进行数值模拟。对比结果表明, 多级渐扩型燃烧室结构能够明显地减小燃烧室压力波动幅度, 提高氢氧燃烧稳定性; 多级渐扩型燃烧室内形成回流区, 可以减小气流轴向运动速度; 火焰扩展形态与渐扩型结构相吻合, 燃烧反应区表面变化平稳; 多级渐扩型燃烧室结构对氢氧火焰传播过程和压力波动现象有着重要影响。