Study on Breakup of Conical Liquid Sheet under Varying Flow Conditions

An experimental study on the breakup of a conical liquid sheet from a pressure swirl atomizer was conducted by using a Particle Image Velocimetry (PIV) system. The variation of wavelength, wave speed and amplitude of wave versus liquid pressure was obtained. The results indicate that the cone half angle increases with liquid pressure. The stripped half wavelength liquid fragment seems to break into a series of drops immediately and no obvious contraction from liquid fragment to ligament is seen. The recorded images also show that both short and long wavelength waves exist simultaneously, and influence the breakup of the conical liquid sheet. The result of this study is useful for the purpose of developing and verifying the atomization model of spray produced by a pressure swirl atomizer.

Development of an ultrathin liquid sheet target for laser ion acceleration at high repetition rates in the kilohertz range

A colliding microjet liquid sheet target system was developed and tested for pairs of round nozzles of 10,11 and 18μm in diameter.The sheet's position stability was found to be better than a few micrometers.Upon interaction with 50 mJ laser pulses,the 18μm jet has a resonance amplitude of 16μm at a repetition rate of 33 Hz,while towards 100 Hz it converges to 10μm for all nozzles.A white-light interferometric system was developed to measure the liquid sheet thickness in the target chamber both in air and in vacuum,with a measurement range of 182 nm±1μm and an accuracy of±3%.The overall shape and 3D shape of the sheet follow the Hasson±Peck model in air.In vacuum versus air,the sheet gradually loses 10%of its thickness,so the thinnest sheet achieved was below 200 nm at a vacuum level of 10±4mbar,and remained stable for several hours of operation.

A comprehensive diagnostic system of ultra-thin liquid sheet targets

To meet the demands of laser-ion acceleration at a high repetition rate,we have developed a comprehensive diagnostic system for real-time and in situ monitoring of liquid sheet targets(LSTs).The spatially resolved rapid characterizations of an LST’s thickness,flatness,tilt angle and position are fulfilled by different subsystems with high accuracy.With the help of the diagnostic system,we reveal the dependence of thickness distribution on collision parameters and report the 238-nm liquid sheet generated by the collision of two liquid jets.Control methods for the flatness and tilt angle of LSTs have also been provided,which are essential for applications of laser-driven ion acceleration and others.

Approximate solutions for the problem of liquid film flow over an unsteady stretching sheet with thermal radiation and magnetic field

The proposed method is based on replacement of the unknown function by a truncated series of the shifted Legendre polynomial expansion. An approximate formula of the integer derivative is introduced. Special attention is given to study the convergence analysis and derive an upper bound of the error for the presented approximate formula. The introduced method converts the proposed equation by means of collocation points to a system of algebraic equations with shifted Legendre coefficients. Thus, after solving this system of equations, the shifted Legendre coefficients are obtained. This efficient numerical method is used to solve the system of ordinary differential equations which describe the thin film flow and heat transfer with the effects of the thermal radiation, magnetic field, and slip velocity.

Atomization mechanism of a charged viscoelastic liquid sheet

In order to study atomization mechanism of a viscoelastic liquid sheet in an electric field, the spatial-temporal stability analysis of a viscoelastic liquid sheet injected into a dielectric station- ary ambient gas in the presence of a vertical electric field is conducted. The dispersion relations of both sinuous and varicose disturbance modes are solved to explore the spatial-temporal instability of a charged viscoelastic sheet, by setting both the wave number and frequency complex. A para- metric study is performed to test the influence of the dimensionless parameters on the absolute instability of the sheet. The results show that the increase of liquid Weber number and time constant ratio, or decrease of gas to liquid density ratio and Reynolds number, can damp the absolute insta- bility. The effect of the liquid elasticity depends on the value of time constant ratio： when time con- stant ratio is small, the increase of liquid elasticity could amplify absolute growth rate, but the effect is weak when the elasticity number is relatively large; when time constant ratio is large, the increase of liquid elasticity cannot affect the absolute growth rate. Moreover, the variation of electrical Euler number can hardly influence the absolute instability of a charged viscoelastic sheet.

Transport Behaviour of La^（3＋） with Flat－Sheet－Sandwich Supported Liquid Membrane Extraction System

This paper suggested a modified model of SLM which could improve its stability.In the model, an organic solution was sandwiched between two layers of supported film,which we called sandwich supported liquid membrane(SSLM).The transport experiments of La3+ were performed with SSLM containing HEH(EHP)as a carrier. The permeability coefficient (p) of La3+ were measured and some factors affecting the p were investigated. The results showed that if the pH of the feed was below 4.0,the p was increased with increasing in pH. The p was also increased when the strip acidity increases.Inspite of not enough satisfactory reproducibility on test result, the stability of the model was improved.

NUMERICAL VALIDATION OF COMPUTATIONAL MODEL FOR SHEET CAVITATING FLOWS

A computational modeling for the sheet cavitating flows is presented. The cavitation model is implemented in a viscous Navier-Stokes solver. The cavity interface and shape are determined using an iterative procedure matching the cavity surface to a constant pressure boundary. The pressure distribution, as well as its gradient on the wall, is taken into account in updating the cavity shape iteratively. Numerical computations are performed for the sheet cavitating flows at a range of cavitation numbers across the hemispheric headform/cylinder body with different grid numbers. The influence of the relaxation factor in the cavity shape updating scheme for the algorithm accuracy and reliability is conducted through comparison with other two cavity shape updating numerical schemes. The results obtained are reasonable and the iterative procedure of cavity shape updating is quite stable, which demonstrate the superiority of the proposed cavitation model and algorithms.

基于鼓泡-引射耦合的柴油初次雾化

针对斯特林发动机小负荷燃油雾化不良问题,提出了基于鼓泡-引射耦合的雾化方式.基于VOF(Volume of Fluid)仿真研究了鼓泡喷嘴内气液流态,并依据时间线性稳定性分析,对射流液膜失稳和破碎进行数学描述,建立了鼓泡-引射耦合下的初次雾化模型.分析了气液质量比RGL(gas-liquid mass ratio)、负荷对初次雾化的影响,并与传统雾化方式比较.结果表明:增大RGL会促进射流失稳、减小液滴粒径.相较于传统雾化方式,鼓泡-引射耦合下小负荷索特平均直径SMD减小约62%,雾化质量显著提高.

浇铸温度对1070A/2024铝合金铸轧复合薄板组织和性能的影响

采用立式双辊铸轧机制备了浇铸温度分别为670、680、690和700℃液-固铸轧1070A/2024铝合金复合板,通过金相显微镜(OM)、X射线衍射仪(XRD)、扫描电镜(SEM)、能谱仪(EDS)等检测设备以及剪切等试验方法,研究了浇铸温度对液-固铸轧1070A/2024铝合金复合板界面组织与性能的影响。结果表明:随着浇注温度的增加,覆层金属逐渐由细小的柱状晶变为粗大的等轴晶;当浇注温度为680℃时,界面处生成少量的金属间化合物,复合板界面结合得最紧密,此时复合界面的显微硬度和剪切强度分别为90.1 HV、86.8 MPa。

不等径开放式撞击流雾化特征及二乙二醇/水体系混合研究

采用粒子图像测速技术(PIV)对不等径开放式撞击流中质量分数60%的甘油‑水溶液雾化性能进行了研究,探讨韦伯数We(51≤We≤1605)、入射速度u(2.12 m·s^(-1)≤u≤6.37 m·s^(-1))、喷嘴直径(喷嘴1:左侧喷嘴直径(D_(1))=1.5 mm,右侧喷嘴直径(D_(2))=2 mm;喷嘴2:D_(1)=2 mm,D_(2)=3 mm)对液膜破碎特征及液滴行为的影响,并对复合含能材料粘结剂溶剂二乙二醇与水混合过程的液滴分布进行了研究。结果表明:随着We增大,液膜破碎长度先增大,当液膜破碎模式到达无边缘模式后减小,且液膜厚度与液滴直径逐步减小,液滴速度逐步增大;随喷嘴直径增大,液膜破碎模式变化不显著,液膜破碎长度、厚度、液滴直径均增大,液滴速度则逐步减小。同时,拟合得到液膜破碎长度、液膜厚度、液滴索特平均直径D[3,2]与喷嘴直径、韦伯数间的经验关联式,采用二乙二醇与水体系验证后发现,随入射速度增大,二乙二醇与水撞击混合后液滴直径减小,分布变窄,D[3,2]数值在经验关联式±15%误差范围内与理论预测结果一致。

固态基板表面硬化层对液-固铸轧1070A/7075复合板组织与性能影响研究

采用钎焊金刚石碗磨片、钢丝刷和百叶片3种不同材料对7075铝合金基板进行打磨,制备了具有不同表面加工硬化层状态的7075铝合金基板,之后采用液-固铸轧的方式制备出1070A/7075铝合金复合板,探究了不同打磨方式下加工硬化层状态对1070A/7075铝合金复合板组织与性能的影响。研究结果表明:3种机械打磨方式下复合板硬化层厚度情况分别为百叶片(45μm)>钢丝刷(25μm)>钎焊金刚石碗磨片(15μm),固态基板经钎焊金刚石碗磨片打磨处理后的1070A/7075铝合金复合板元素扩散距离为7.5μm,结合强度为55.2 MPa。

4343/3003/4343铝合金钎焊板固-液-固铸轧复合制备工艺研究

基于双辊铸轧复合技术,提出了4343/3003/4343铝合金钎焊板的固-液-固双辊铸轧复合工艺,并实现了3.65 mm厚铸轧复合板在实验室条件下的制备,随后将其冷轧至目标厚度0.5 mm,对铸轧复合板的微观组织进行了SEM和能谱分析(EDS)研究,对轧制成品复合带的包覆率与拉伸性能进行了测试。结果表明:铸轧复合铝板的界面平整,无空隙、杂质缺陷存在,芯材与覆层之间存在1.4μm的扩散层,两者的结合为冶金结合。复合带的包覆率为9.97%,偏差为±0.15%,抗拉强度为234.8MPa,伸长率为3.74%,满足国家标准要求。采用固-液-固固铸轧复合工艺能够快速实现芯材与覆层的冶金结合,同时铸轧出口厚度较小,轧制到成品所需道次少,具有生产效率高、能耗低、成本低等优势。

贝塞尔双光子光片显微镜在活体生物成像中的应用

双光子光片显微镜具有分辨率高、光漂白低等优势,在生物学领域有着广泛的应用。但由于照明光片厚度与长度之间的取舍矛盾问题,导致轴向分辨率和成像视场无法兼顾,因此在应用中受到限制。为了解决这一问题,本文采用液晶空间光调制器将普通高斯照明光束调制为贝塞尔光束,利用贝塞尔光束的“无衍射”特性实现了大且薄的光片照明,光片长度与厚度之比达到了163。在此基础上,设计并搭建了一套贝塞尔双光子光片显微镜,在310μm的视场范围内实现了横向440 nm、轴向1.9μm的三维高分辨率成像。本文成功实现了斑马鱼胚胎的活体成像,可以做到血液细胞流速的测量和脊柱骨细胞的分割计数,验证了贝塞尔双光子光片显微镜在活体生物成像中的应用潜力。

非常规货币政策退出的溢出效应分析

随着全球经济从新冠疫情带来的冲击中逐渐复苏,美国等发达经济体逐步退出疫情期间大量使用的非常规货币政策,导致本国的利率上升以及市场流动性收缩。这可能吸引资本回流,对他国金融市场造成冲击。理论层面,基于蒙代尔弗莱明模型通过阐述非常规货币政策溢出效应的传导机制,分析政策退出可能产生的外溢影响。实证方面,文章运用VAR模型分析新冠疫情后美国退出非常规货币政策对我国货币市场、债券市场以及外汇市场的溢出效应。结论:美联储加息会推动我国国债收益率、同业拆借利率上升,汇率贬值;缩表会导致汇率人民币汇率贬值。总体来看,美联储加息对我国金融市场的影响较显著且更为直接,缩表的影响则较小且存在一定的滞后影响。在美联储逐渐退出非常规货币政策过程中,加息对我国金融市场的外溢效应更为显著,应着重采取政策加以防范风险。

流动性视角下中国银行业系统性风险的测度

基于2011—2019年中国商业银行的资产负债表数据,结合Bootstrap法,使用流动性剩余指标估计商业银行的流动性风险,利用风险贡献度指标计算商业银行的系统重要性。研究表明:样本中的绝大多数银行2016年、2017年的相对流动性剩余高于其9年间的均值,其余年份基本低于均值,说明在2015年股市危机后,宽松的经济政策降低了银行的流动性风险。中国工商银行、中国建设银行、中国银行、中国农业银行是国内系统重要性银行,风险贡献度合计高达77.4%。研究结论为银行业防范系统性风险提供参考。

机械表面处理对液-固铸轧1070A/7075复合板结合性能的影响

通过激光共聚焦扫描显微镜(LSCM)、扫描电镜(SEM)、能谱仪(EDS)等检测仪器及拉剪试验,研究了机械表面处理方向对7075铝合金板材形貌及1070A/7075复合板结合性能的影响。研究结果表明:平行于铸轧方向对固态基板进行机械打磨,其板材粗糙度(9.3μm)高于垂直铸轧方向打磨的板材(8.5μm),且复合板界面处未发现氧化物,复合板结合强度为54.7 MPa。在液-固铸轧制备复合板时,应选择平行于铸轧方向对固态基板进行机械打磨。

退火温度对液-固铸轧1070A/7075复合板组织与性能的影响

通过金相显微镜(OM)、扫描电镜(SEM)、能谱仪(EDS)等检测设备以及拉伸和剪切等试验方法,研究了退火温度对液-固铸轧1070A/7075复合板材组织与性能的影响。结果表明:随着退火温度的不断提高,复合板材界面7075固态基板一侧开始出现连续的带状结构组织,抗拉强度与屈服强度不断下降,延伸率不断增加,剪切强度不断增大。当退火温度为400℃时,元素扩散距离与剪切强度均达到最大值,分别为37μm与114.3 MPa。

基于SPH方法的射流撞击仿真

为了研究液体推进剂的撞击雾化问题,采取光滑粒子流体动力学方法 (SPH)进行了射流撞击形成液膜过程的数值模拟。修正了基于连续表面力模型的表面张力算法,推导了考虑粘性与表面张力作用的SPH形式的控制方程,对撞击雾化模型进行了合理简化,采用水作为推进剂模拟液。得到了不同撞击速度、角度下的液膜图像及液膜的形成过程图像。证明了SPH方法适于解决存在自由表面及大变形的射流撞击问题。

射流撞击雾化液滴运动过程与粒径分布特性的试验研究

在大气环境下,以水为介质,采用PDPA和高速动态分析系统,针对直流撞击式喷注单元的雾场结构进行试验研究,获得了雾化液滴速度分布、粒径分布等试验参数。从液滴运动及液滴大小分布的角度针对撞击雾化液膜破碎成液滴的过程进行了分析,发现水平面上雾化液滴的径向速度以原点为中心对称,且随离原点距离增大而增大;初始雾化阶段的粒径大小分布则与径向速度分布相反。分析认为是液膜运动过程赋予了雾化液滴的初始速度,并影响了初始雾化液滴的分布特性。

加热条件下液膜射流破碎尺度影响因素的研究

利用线性不稳定性理论对加热条件下粘性液膜射流模型所对应的色散方程进行了数值求解。利用得到的计算结果研究了加热条件下无量纲数对液膜射流破碎尺度的影响。结果表明:在反对称模式下,当We·Q<1时,液膜破碎处于大尺度模式,反之则处于小尺度模式;在对称模式下,当We·Q<1且Ma<Macri时,液膜破碎处于大尺度模式,反之则处于小尺度模式。