Numerical analysis of spatial evolution of the small signal gain in a chemical oxygen-iodine laser operating without primary buffer gas

A chemical oxygen iodine laser (COIL) that operates without primary buffer gas has become a new way of facilitating the compact integration of laser systems. To clarify the properties of spatial gain distribution, three-dimensional (3-D) computational fluid dynamics (CFD) technology was used to study the mixing and reactive flow in a COIL nozzle with an interleaving jet configuration in the supersonic section. The results show that the molecular iodine fraction in the secondary flow has a notable effect on the spatial distribution of the small signal gain. The rich iodine condition produces some negative gain regions along the jet trajectory, while the lean iodine condition slows down the development of the gain in the streamwise direction. It is also found that the new configuration of an interleaving jet helps form a reasonable gain field under appropriate operation conditions. (c) 2007 Elsevier Ltd. All rights reserved.

Numerical modeling of 3-D turbulent two-phase flow and coal combustion in a pulverized-coal combustor

In the present paper, a multifluid model of two-phase flows with pulverized-coal combustion, based on a continuum-trajectory model with reacting particle phase, is developed and employed to simulate the 3-D turbulent two-phase hows and combustion in a new type of pulverized-coal combustor with one primary-air jet placed along the wall of the combustor. The results show that: (1) this continuum-trajectory model with reacting particle phase can be used in practical engineering to qualitatively predict the flame stability, concentrations of gas species, possibilities of slag formation and soot deposition, etc.; (2) large recirculation zones can be created in the combustor, which is favorable to the ignition and flame stabilization.

A characteristics study on the performance of a 2-stage light gas gun

In order to obtain an overall and systematic understanding of the performance of a two-stage light gas gun (TLGG), a numerical code to simulate the process occurring in a gun shot is advanced based on the quasi-one-dimensional unsteady equations of motion with the real gas effect,;friction and heat transfer taken into account in a characteristic formulation for both driver and propellant gas. Comparisons of projectile velocities and projectile pressures along the barrel with experimental results from JET (Joint European Tons) and with computational data got by the Lagrangian method indicate that this code can provide results with good accuracy over a wide range of gun geometry and loading conditions.

Hierarchal structure of the simplified Navier-Stokes equations (SNSE) and its mechanical connotation and application

The hierarchial structure and mathematical property of the simplified Navier-Stokesequations (SNSE) are studied for viscous flow over a sphere and a jet of compressible flu-id. All kinds of the hierarchial SNSE can be divided into three types according to theirmathematical property and also into five groups according to their physical content. Amultilayers structure model for viscous shear flow with a main stream direction is pre-sented. For the example of viscous incompressible flow over a flat plate there existthree layers for both the separated flow and the attached flow; the character of thetransition from the three layers of attached flow to those of separated flow is elucidated.A concept of transition layer being situated between the viscous layer and inviscidlayer is introduced. The transition layer features the interaction between viscous flow andinviscid flow. The inner-outer-layers-matched SNSE proposed by the present author inthe past is developed into the layers matched (LsM)-SNSE.

采用偏置射流预燃室稳定燃烧水煤浆的原理及应用研究

水煤浆作为经济型清洁燃料引起人们的长期关注。水煤浆偏置射流预燃室具有对浆种适应性强，稳燃性能好等特点。本文对偏置射流预燃室稳定燃烧水煤浆的原理进行了探讨，并对该燃烧技术用于处理造纸黑液的研究情况作了介绍。结果表明，采用低压多级雾化喷嘴对水煤浆进行雾化，形成的雾炬和偏置射流预燃室的流场有良好的匹配，在预燃室内形成大尺度的回流区，有利于煤浆的点火、稳燃和消除灰渣。

超声速燃烧室凹腔火焰稳定器的数值模拟

为分析凹腔火焰稳定器在超声速燃烧室中的流动特性,运用数值模拟方法研究了凹腔对H2超声速燃烧的作用规律。通过对比分析不同凹腔长深比L/Du,后缘倾角θ,后缘深度D_d和H_2喷射位置Ljet对燃烧室性能的影响,发现凹腔的火焰稳定机制主要在于富含自由基的高温回流区;L/D_u=7-9,θ=30°,D_u/D_d=1.0和L_(jet)=24mm的燃烧室强化混合燃烧的性能较好,可以获得较高的燃烧效率和总压恢复。

航天运载器尾舱高空热环境数值分析

航天运载器在70km以上高空高速飞行，火箭发动机的喷流是影响其尾舱热环境的主要因素之一。采用代数方程和偏微分方程相结合的多块网格生成方法，达到热流计算中对近壁面网格的正交性和分布上的要求；通过改进的NND有限体积法高超程序，数值耦合求解多组分NS方程、湍流方程、热辐射方程和非平衡化学反应方程，提高了壁面热流计算的精度。计算结果与飞行遥测及地面实验结果对比分析表明，所采用的计算方法及得到的结果是正确有效的。

欠膨胀超声速射流不稳定性机理的数值研究

应用NND有限差分格式求解轴对称可压缩N-S方程,研究了不同驻室与环境压力比条件下欠膨胀超声速射流近场的失稳特性.计算结果表明欠膨胀超声速射流的失稳机制根据射流激波结构的特征可分为3种失稳模式:具有规则反射激波结构和单一剪切层特征的射流不稳定性;带有马赫反射激波结构和双剪切层特征的射流不稳定性;具有弯曲马赫杆和高度欠膨胀射流的不稳定性.对于欠膨胀超声速射流,沿射流方向重复出现拟周期性的射流激波结构是射流稳定发展的特征,这种射流激波结构的消失是射流开始失稳的标志.

水射流辅助破岩机理研究(2)——水滴撞击

利用MSC.Dytran中的具有强度的多材料欧拉网格模拟水滴和有限长连续射流对靶板(岩石)的高速冲击作用,研究了靶板破坏深度、破坏宽度与水滴初压力、速度、入射方向、板厚以及连续射流的密度等的关系及其物理意义.用应力波理论来解释靶板的层裂现象,试图多角度分析射流破岩机理.

探针移动速度对等离子体射流热流密度测量结果的影响

采用自行研制的中心嵌有铜柱感应件的小尺寸杆状热流探针,在低扰动条件下,对射入大气环境的纯氩层流等离子体射流传向铜探头表面的热流密度进行了动态测量。结果表明,在射流最高温度16500 K、最大轴向速度850 m/s、探针垂直于射流流动方向的移动速度130～260 mm/s的实验参数范围内,随着探针移动速度的提高,测得的热流密度值减小;射流温度和速度越高,探针移动速度对热流密度测量值的影响越大。

支板凹腔一体化超燃冲压发动机实验研究

本文针对以凹腔支板一体化燃烧室为基本结构的超燃冲压模型发动机在自由射流风洞中的性能，主要研究了燃料在不同位置喷入时，燃烧室几何结构／气动性能／燃料混合及燃烧特性的相互耦合，以及对发动机推力性能的影响。结果表明支板与凹腔的一体化在合理配置燃料分布情况下可以获得较好的发动机性能。

煤油射流在超声速燃烧室中的实验研究

在超声速燃烧室中分别采用气泡雾化煤油与纯煤油射流进行实验,研究不同情况对燃料的雾化和贯穿深度的影响.实验选用纹影法记录实验段图像,拍摄了不同注射压强条件下燃料有无气泡雾化的流场照片,对时间平均流场和瞬态流场分别进行记录.实验结果表明:气泡雾化的确明显地提高了液体燃料的雾化程度,但对贯穿深度没有显著的影响,提高贯穿深度的有效方法是增加射流压强.

高超声速流动中侧向喷流干扰特性的实验研究

在高超声速(M=6)流动中,实验研究了侧向喷流的干扰特性,并探讨了喷流压力、攻角、迎风侧及背风侧喷流对侧向喷流干扰特性的影响.结果表明,在高超声速流动中,随喷流压力增大,喷流弓形激波与来流弓形激波相交,喷流前的高压区增大,而喷流后的低压区几乎不受影响,喷流的控制效果加强.与迎风侧喷流相比,背风侧喷流控制效果更好,这一趋势随攻角的增大更加明显.

脉冲液体射流泵性能的理论分析及数值计算

推导了以往复泵为脉冲发生装置的脉冲液体射流泵准二维性能方程及其时均性能方程,导出无因次惯性水头及惯性力项便于计算的表达式,并对脉冲液体射流泵时均性能进行了数值计算,计算结果与试验数据基本吻合,将数值计算的模拟曲线与恒定液体射流泵性能曲线进行对照,证明了采用脉冲射流作为工作动力能够大幅提高射流泵的效率.

超音速流动中侧向喷流干扰特性的实验研究

在超音速流动中,进行了侧向喷流干扰特性的实验研究,研究了喷流压力、攻角、迎风侧及背风侧喷流对侧向喷流干扰特性的影响.结果表明,随喷流压力增大,喷流前的高压区向前扩展,喷流的包裹作用加强.有攻角时,背风侧喷流前的高压区更大,喷流包裹作用的影响区域前移,喷流的控制效果更好,这一趋势随攻角的增大更加明显.