激光产生蒸汽羽的干涉研究

 根据拍摄1.06 μm长脉冲钕玻璃激光与LY12铝靶耦合产生蒸汽羽的干涉分幅照片，测出在t<50 μs空气冲击波速度约为473 m/s而蒸汽羽阵面扩散速度约为162 m/s。运用蒸汽羽等离子体的有关热力学特性方程组，得到蒸汽羽等离子体的电子密度、电子温度、电离度和吸收系数的最大值分别为N_e≈3.1×10¹⁷ cm^-1，T≈6 096 K，η≈0.014，α_(1.06μm)≈0.03 cm^-1的结果。     

长脉冲激光辐照LY—12铝靶烧蚀表面的后退速度

用烧穿靶法测量自由振荡长脉冲 1.06μm会聚激光束烧蚀LY-12铝合金靶时间,用电子微量天平、金相显微仪、收集器等测量激光烧蚀铝靶材参量Am和h的技术,给出激光束烧蚀铝靶的烧蚀表面后退速度和烧蚀速度的结果。当烧蚀靶材的激光通量I=10~5～10~7W/cm~2时,烧蚀表面后退速度为0.5～3.8m/s,烧蚀速度为 1～8g/s。     

高速弹体对钢筋混凝土靶的侵彻/贯穿效应实验研究

为了研究高速弹体对钢筋混凝土靶的侵彻/贯穿效应,以100 mm口径滑膛炮作为发射平台,驱动10 kg级卵形弹体以820～1195 m/s速度撞击强度为31.0～43.6 MPa的钢筋混凝土靶,获得了弹体侵彻/贯穿钢筋混凝土靶的终点弹道实验数据,并对弹体的侵彻/贯穿深度、靶板侧面自由面效应、弹体的变形进行了详细分析。结果表明:弹体的侵彻/贯穿深度为2.2～2.8 m,部分经验公式预估的侵彻/贯穿深度与实验结果吻合较好;当靶面相对尺寸较小且弹速较高时,靶板侧面自由面效应比较明显;当弹速达到1195 m/s时,弹体开始由刚体向半流体转变。     

SPH方法在宽速域岩石侵彻问题中的应用

采用光滑粒子流体动力学(SPH)方法对花岗岩靶板受碰撞侵彻的大应变、高应变率变形问题进行了数值模拟。为了描述弹目材料的非线性变形及破坏特性,对花岗岩靶板引入了Holmquist-Johnson-Cook(HJC)本构模型及损伤模型,对弹体引入含损伤的Johnson-Cook(J-C)本构方程和Grüneisen状态方程,靶板与弹体均离散成拉格朗日粒子。通过自编程序仿真计算0～4 m/s的着靶速度下花岗岩靶板的三维侵彻过程,对比分析了钢珠在不同弹体条件下的侵彻结果,在固体侵彻、半流体侵彻和流体侵彻的区域内拟合了侵彻深度随着靶速度的变化曲线。数值计算结果显示,侵彻深度随着靶速度的增加在固体侵彻区间(v01421 m/s)呈现递增趋势,在半流体侵彻区间(1421 m/s?v0?1700 m/s)呈现递减趋势,在流体侵彻区间(v0 1700 m/s)呈现递增趋势并逐渐趋于平滑,达到峰值。     

激光辐照下金属靶表面汽化现象研究

用高速纹影诊断技术研究激光辐照下金属表面发生汽化的特征及蒸气发展运动过程,结合汽化模型给出了凝聚相表面温度与激光入射功率密度的关系。由实验得到了不同入射激光功率密度下汽化表面(凝聚相)温度,蒸气羽阵面速度,前驱空气冲击波速度。     

空间碎片典型材料激光烧蚀反喷羽流实验研究

建立了观测和记录不同激光入射角度烧蚀6061铝合金靶材等离子体反喷羽流特性的实验装置,对实验结果图像进行了处理,并对处理结果进行了数值拟合。拟合结果表明,激光辐照靶材后100ns内,等离子体反喷羽流大致分布区域为靶面外5mm×5mm。激光以不同角度入射时,等离子体反喷速度相对于靶面法线方向大致呈轴对称分布。当激光相对靶面法线方向小角度范围内入射时,激光烧蚀引起的冲量主要沿靶面法线方向,反喷羽流沿靶面法方向的速度为20~40km·s-1。激光斜入射时,反喷羽流沿靶面法线方向的速度要大于激光垂直入射的情况。高斯函数可以很好地描述等离子体反喷羽流速度分布。     

锁定放大器在光速测量中的应用

结合声光调制原理和锁定放大器的工作原理,设计了基于调制法的测量光速实验.通过测量和计算得出光速为2.993×108 m/s和3.000×108 m/s,与光在空气中的速度值2.997×108 m/s相比,误差分别为0.13%和0.10%.此方法的优点是光速经过调制后,光的频率被调制为60～100 MHz,使得光波长调制为3～5 m,便于在实验室里进行光速测量.     

超空泡射弹水下侵彻靶板三相耦合数值模拟

超空泡射弹侵彻问题的实质是特殊水下结构受到高速冲击载荷作用下的动态响应。对12.7 mm口径超空泡射弹侵彻典型水下目标壳体的毁伤效果开展研究,基于LS-DYNA有限元分析软件建立水环境中超空泡射弹垂直侵彻曲面靶板的等效模型,探讨射弹侵彻过程中动能侵彻和气泡溃灭对靶板联合毁伤效果,获得了靶板在各阶段的应力变化和结构变形规律。结果表明:侵彻靶板前,射弹着靶速度为200 m/s时的头部表面水介质压力峰值达768 N,靶板表面有明显下凹变形;侵彻靶板时,伴随着射弹动能侵彻和气泡溃灭冲击,水介质造成的影响不足动能侵彻的2%;侵彻靶板后,在靶板正面形成峰值速度为42 m/s的水射流进一步作用于破口;靶板整体弯曲变形,在200~300 m/s范围内,随着射弹着靶速度的增加,靶板弯曲形变量减小;靶板局部发生延性穿孔,射弹在水环境中具有更好的破口效果,射弹速度变化对破口尺寸影响不大。     

强流脉冲离子束辐照靶材烧蚀效应二维数值研究

对强流脉冲离子束(IPIB)辐照Ti靶的烧蚀效应进行了二维数值研究.得到了表面烧蚀物质随脉冲时间的变化关系.得出TEMP Ⅱ 型加速器产生的脉冲束流辐照靶材时引起的汽、液化均是从表面开始、并且汽化过程中表面物质被层层烧蚀的结论.同时，得到中心区的平均烧蚀速度为10m/s 数量级，它远小于产生的烧蚀等离子体的喷发速度.得到脉冲期间靶材内部不同位置烧蚀斑痕形状的时间演化过程，以及束流中含有的离子种类分额不同时IPIB辐照过程产生的不同效果. 关键词： 强流脉冲离子束 靶 烧蚀过程 二维数值模拟     

运动状态下聚能战斗部侵彻披挂反应装甲靶板的数值模拟

运用LS-DYNA有限元程序模拟了不同横向飞行速度(150、200、300、400、500m/s)和侵彻角度(30°、45°、60°)情况下聚能战斗部对披挂反应装甲后效靶板的侵彻过程,讨论了射流所受干扰情况及其对后效靶板的侵彻结果。研究结果表明:当侵彻角度一定时,射流对靶板表面的切割长度随速度的增大而增大,且在侵彻角度为30°时增大速率最快;但射流侵彻深度随速度的增大而减小,且在侵彻角度为60°时减小速率最慢。当飞行速度一定时,射流对靶板表面的切割长度和侵彻深度均随侵彻角度的增大而减小,且表面切割长度降幅随速度的增大呈先增大后减小的趋势,在速度为300m/s时,降幅最大,为59.6%;而侵彻深度降幅随速度的增大呈先减小后增大的趋势,在速度为350m/s时,降幅最小,为39.3%。最后通过理论方法分析了数值模拟结果,论证了数值模拟方法的正确性。     

Study of the plume generated by Nd:YAG laser ablation of a hydroxyapatite target

The plume generated by Nd:YAG laser ablation of a hydroxyapatite target has been investigated in vacuum and at 0.1 and 0.2 mbar of water vapor. The investigation has been carried out by means of fast intensified CCD imaging with the aid of bandpass interferential filters that allow the following single species to be isolated: neutral calcium, calcium oxide radicals and neutral oxygen. Results obtained in vacuum reveal that expansion takes place at a constant velocity of about 2᎒⁴ m/s for the atomic species and about 3᎒³ m/s for the molecular ones and that emission is completely dominated by emissive neutral calcium. When ablation is carried out in a water atmosphere, the background gas confines the species in the leading edge of the plume, which results in the formation of a planar shock wave at 0.1 mbar and a spherical shock wave at 0.2 mbar. Comparison of the images with those obtained at 0.1 mbar of Ne has revealed the existence of chemical reactions between the plume and the water atmosphere, leading to the formation of calcium oxide radicals. In that case, plume emission is dominated by these molecular species.     

Influence of ambient pressure on the performance of an arc discharge plasma actuator

The arc discharge plasma actuator (ADPA) has wide application prospects in high‐speed flow control because of its local heating effect and strong disturbance. In this paper, the influence of ambient pressure, which ranges from 3 to 20 kPa, on the performance of a two‐electrode ADPA is investigated by a schlieren system. The duration of the arc heated region, as well as its area, is extracted by image processing. As the ambient pressure increases, different flow field evolutions occur. The duration of the ADPA heated region increases with the ambient pressure. The maximum duration reaches 1185.3 µs at 20 kPa. The velocity of the discharge‐induced blast shock wave first decreases gradually and then remains at 345 m/s for all air pressures. The blast shock wave has a higher velocity at lower pressures when it is freshly produced. A maximum blast shock wave velocity of 582 m/s is observed at the pressure of 7 kPa. The arc heated region is not sensitive to ambient pressure, but the deposited energy from the arc increases when the pressure increases.     

高超声速飞行目标尾焰红外辐射测量

为了研究超高声速飞行器发动机尾焰喷射高温高速气流的辐射特性,对尾焰成分CO₂及H₂O分子在4.3和2.7 μm大气窗口红外辐射波段进行了测量.利用高温燃气激波风洞模拟产生超高声速飞行器尾焰喷流,喷流速度M=5.5.实验中选用单元型InSb红外探测器,并利用黑体进行原位定标.测量距离为0.7 m,采用单透镜成像加光阑的方法收集光信号.实验中分别沿喷流方向喷流垂直方向进行了多点测量,通过定标结果反演得到尾焰在4.3和2.7 μm分别沿喷流方向和喷流垂直方向的光谱辐亮度和波段辐亮度分布,测量结果表明4.3 μm辐射强度及稳定性均高于2.7 μm.      

Influence of air pressure on the performance of plasma synthetic jet actuator

Plasma synthetic jet actuator(PSJA) has a wide application prospect in the high-speed flow control field for its high jet velocity.In this paper,the influence of the air pressure on the performance of a two-electrode PSJA is investigated by the schlieren method in a large range from 7 k Pa to 100 k Pa.The energy consumed by the PSJA is roughly the same for all the pressure levels.Traces of the precursor shock wave velocity and the jet front velocity vary a lot for different pressures.The precursor shock wave velocity first decreases gradually and then remains at 345 m/s as the air pressure increases.The peak jet front velocity always appears at the first appearance of a jet,and it decreases gradually with the increase of the air pressure.A maximum precursor shock wave velocity of 520 m/s and a maximum jet front velocity of 440 m/s are observed at the pressure of 7 k Pa.The averaged jet velocity in one period ranges from 44 m/s to 54 m/s for all air pressures,and it drops with the rising of the air pressure.High velocities of the precursor shock wave and the jet front indicate that this type of PSJA can still be used to influence the high-speed flow field at 7 k Pa.     

Analysis of hydroxyapatite laser ablation plumes in a water atmosphere

4 m/s, shows the development of a shock wave in its front, resulting from the interaction between the species released from the target and the background gas. The water vapor slows down this component up to values of about 3×10³ m/s following a behavior that can be well described by the dynamics of a spherical shock wave. The low intensity of emission of the second component has not allowed us to analyze its dynamics. The third and slowest component expands at a constant velocity of 5×10² m/s and is constituted by hot particulates leaving the target. Spectra recorded in the shock front have shown the presence of emission lines arising from Ca I, Ca II, P I and some impurities, and two strong emission bands that can be assigned to some sort of calcium oxide. Received: 7 November 1997/Accepted: 17 February 1998     

流速对混合蒸汽Marangoni凝结换热影响的实验研究

本文在蒸汽压力为47.36 kPa的条件下,通过实验研究了不同蒸汽流速(u=2、4、5 m/s)下纯水和不同酒精浓度水-酒精混合蒸汽沿重力方向流过竖直紫铜平板表面上的凝结换热特性,并实现了实验的可视化,同时分析了不同蒸汽流速下造成Marangoni凝结换热特性差异的原因.实验及分析结果表明,在相同蒸汽浓度、蒸汽压力和表面过冷度条件下,高流速下的凝结换热系数比低流速的大.且蒸汽流速对凝结换热的影响因混合蒸汽酒精浓度的不同而不同,低浓度0.5%和高浓度50%时流速的增加对凝结换热特性的影响较小,而在中间浓度2%时凝结换热强度随流速的增加明显.     

Generation of blast waves in a channel by nonideal detonation of aluminum-enriched high-density compositions

The results of experimental studies of the nonideal detonation of high-density, high-energy aluminum-ammonium perchlorate-organic fuel-HE compositions and of the blast waves it generates in a channel filled with air are presented. Aluminum-enriched compositions have high densities (up to 2 g/cm³) and high heats of explosion, nearly twice that for TNT. The studies were performed to work out scientific fundamentals of controlling nonideal detonation and to explore the possibility of creating new high-energy high-density formulations with an enhanced fugacity effect. The factors that enable controlling the nonideal detonation of such charges were determined. It was demonstrated that, at RDX contents above 15%, the detonation velocity increases linearly with the charge density while the critical detonation diameter decreases. Adjusting the density, HE content, ratio of the components makes it possible to vary the detonation velocity in high-density charges over a wide range, from 4 to 7 km/s. The experimental data were compared to the thermodynamically calculated velocity of ideal detonation. For the compositions under study, the pressure- time histories of the blast wave generated in a cylindrical tube by the expanding detonation products at different distances from the charge were measured. The results were compared to analogous data obtained under the same conditions for the detonation of the same mass of TNT (100 g). The parameters of blast waves generated by the test compositions are markedly superior to those characteristic of TNT: the pressure at the leading front of the wave and pressure impulse at a given distance from the charge were found to be 1.5–2.0 (or even more) times those observed for TNT. The TNT equivalency at pressures 30–60 atm has similar values. The TNT equivalencies in pressure and pressure impulse depend nonmonotonically on the distance from the charge, so far unclear why. It was established that the interaction between excess fuel and air oxygen during the expansion of detonation products contributes little to supporting the blast wave.     

XPS studies of short pulse laser interaction with copper

The effect of laser ablation on copper foil irradiated by a short 30 ns laser pulse was investigated by X-ray photoelectron spectroscopy. The laser fluence was varied from 8 to 16.5 J/cm² and the velocity of the laser beam from 10 to 100 mm/s. This range of laser fluence is characterized by a different intensity of laser ablation. The experiments were done in two kinds of ambient atmosphere: air and argon jet gas.The chemical state and composition of the irradiated copper surface were determined using the modified Auger parameter (α′) and O/Cu intensity ratio. The ablation atmosphere was found to influence the size and chemical state of the copper particles deposited from the vapor plume. During irradiation in air atmosphere the copper nanoparticles react with oxygen and water vapor from the air and are deposited in the form of a CuO and Cu(OH)₂ thin film. In argon atmosphere the processed copper surface is oxidized after exposure to air.