Capillary jet instability under the influence of gravity

The focus of this paper is on the effect of gravity stretching on disturbed capillary jet instability. Break-up and droplet formation under low flows are simulated using finite difference solution of a one-dimensional approximation of disturbed capillary jet instability chosen from the work by Eggers and Dupont (J. Fluid Mech. 155 (1994) 289). Experiments were conducted using water and aqueous glycerol solutions to compare with simulations. We use a gravity parameter, G, which quantifies gravity stretching by relating flow velocity, orifice size and acceleration and is the reciprocal of the Froude number. The optimum disturbance frequency was found to be inversely proportional to G. However, this relationship appears to be complex for the range of G's investigated. At low G, the relationship between and G appears to be linear but takes on a weakly decaying like trend as G increases. As flows are lowered, the satellite-free regime decreases, although experimental observation found that merging of main and satellite drops sometimes offset this effect to result in monodispersed droplet trains post break-up. Viscosity did not significantly affect the relationship between the disturbance frequency and G, although satellite drops could be seen more clearly close to the upper limit for instability at high G's. It is possible to define regimes of satellite formation under low flows by considering local wavenumbers at the point of instability.     

Ablation of ice-solids and wax-solids mixtures in turbulent axisymmetric water jets

The ablation rate of frozen mixtures of water or wax with finely divided solids subjected to a turbulent axisymmetric water jet was investigated both experimentally and theoretically. The range of the water jet Reynolds number was 8700–29300 and the jet temperature varied between 22 and 60°C. The solids used were very fine kaolinite clay, titanium oxide and aluminium powder. The type of solids and their concentration were found to affect the ablation rate of ice-solids and wax-solids mixtures. This is mainly due to changes in the physical properties of the melt layer of the water-solids or wax-solids mixtures which forms between the impinging jet and the frozen mixtures.     

Research on the Control Strategy of Variable Nozzle Turbocharger for Natural Gas Engine

A variable nozzle turbocharger (VNT) was applied to a 2.2-liter L4 natural gas engine,and a VNT control system was designed to operate it.Based on VNT matching test results,a VNT control strategy was studied,in which VNT adjustment is carried out through pre-calibrated VNT handling rod position,combined with a closed-loop target boost pressure feedback using proportional-integral-derivative(PID) algorithm.Experimental results showed that the VNT control system presented in this thesis can lead to optimized ...     

Characteristics of shell thickness in a slab continuous casting mold

The key to reduce shell breakout in the continuous casting process is to control shell thickness in the mold.A numerical simulation on the turbulent flow and heat transfer coupled with solidification in the slab mold using the volume of fluid (VOF) model and the enthalpy-porosity scheme was conducted and the emphasis was put upon the flow effect on the shell thickness profiles in longitudinal and transverse directions.The results show that the jet acts a stronger impingement on the shell of narrow face,which causes a zero-increase of shell thickness in a certain range near the impingement point.The thinnest shell on the slab cross-section locates primarily in the center of the narrow face,and secondly near the comer of the wide face.Nozzle optimization can obviously increase the shell thickness and make it more uniform.     

自激振荡脉冲射流的研究与进展

指出了自激振荡脉冲射流的产生机理,概述了国内外主要的研究和应用成果,并对这些成果进行分析后指出：目前的研究方法主要基于经验,基于理论或基于方法;目前主要的应用领域为石油钻井、油罐清淤和渔业充氧等.最后对进一步研究的方向和应用的领域作出了展望,可为相关研究参考.     

喷嘴偏心距对射流泵性能影响的数值模拟

对射流泵内部流动进行了数值模拟,计算了射流泵在不同喷嘴偏心距下的性能参数,分析了射流泵喷嘴轴线偏离泵体轴线的偏心距对其性能和流场的影响.结果表明:喷嘴偏心距对射流泵大流量比工况的性能有较大的影响,而对小流量比工况影响较小,可忽略不计;随着偏心距的增加,射流泵效率最高点下降并向流量比小的方向移动.在工程应用中,射流泵同轴度精度要求可以定为12级以上.     

等离子喷涂枪喷嘴不同水冷方式的数值分析

为了分析等离子喷涂枪喷嘴水冷却系统的冷却效果,减少喷嘴的烧损现象,利用FLUENT数值模拟软件,基于计算流体动力学和数值传热学的方法,采用压力耦合方程组的半隐式算法(即SIMPLE算法),在保持喷嘴水冷却系统结构不变的情况下,设计了第1种水冷方式;通过调换进、出水道位置形成第2种水冷方式;在此基础上,理论设计了另外2种水冷方式,着重建模分析了喷嘴壁面温度场和其不同水冷方式下的速度场.通过比较得出了较合理的水冷方式,减少或消除了冷却死水区域,达到进一步冷却喷嘴的目的,同时分析了后2种方式应用于实际的可行性.分析结果表明,采用数值模拟技术能够比较准确地模拟喷嘴水冷却系统的有关特性,可进一步优化设计喷嘴水冷却系统.     

喷管轴线、摆角等参数的红外光电探测

提出了一种基于多目视觉红外光电探测和圆锥曲面拟合的喷管轴线、摆角等参数估计方法.假定前端装有红外LED发光板和红外滤光片的4台高速相机实现了同步数据采集,且已完成标定.以红外反光标记球贴着喷管表面移动的大量三维坐标采样为基础,采用圆锥曲面拟合的方法求取喷管轴线的向量表示以及喷管圆锥曲面的虚拟顶点.通过喷管摆动的大量瞬时转轴拟合得到最小二乘意义上的摆动轴.将喷管轴线和摆动轴的公垂线与喷管轴线的交点作为摆心.喷管在摆动前后任意两时刻间的摆角可以用喷管上标记点的前后坐标到摆动轴的垂线向量的内积求得.摆角变化量除以时间间隔可得摆动角速度.摆动角速度的变化量除以时间间隔可得摆动角加速度.使用双轴摇摆-直线升降运动校准装置模拟喷管运动,摆心位移、摆角、摆动角速度和角加速度的测量误差分别为0.17mm、0.03°、0.12(°)/s、0.4(°)/s2.实验结果证明了算法的可行性.     

Discrimination for ablative control mechanism in solid-propellant rocket nozzle

The ablation in solid-propellant rocket nozzle is a coupling process resulted by chemistry, heat and mass transfer. Based on the heat and mass transfer theory, the aero-thermo-dynamic, and thermo-chemical kinetics, the thermal-chemical ablation model is established. Simulations are completed on the heat flow field and chemical ablation in the nozzle with different concentrations, frequency factors and activation energy of H2. The calculation results show that the concentration and the activation energy of H...     

油性颜料型彩色喷墨墨水的性能研究

以丙烯酸甲酯,甲基丙烯酸甲酯和丙烯酰胺为单体,经过自由基共聚,再经Hofmann降解反应,合成了带有胺基的丙烯酸酯类的共聚物。将该共聚物作为喷墨墨水中的连接料,达到增强颜料在墨水中的分散稳定性的目的。用红外光谱确定了酰胺基到胺基的转化。测定了带胺基的聚丙烯酸酯的连接料含量与墨水体系稳定性、沉降率的关系。带胺基的聚丙烯酸酯的连接料配制成的墨水,体系稳定性好,置于扫描电镜下观察,颜料具有较好的颗粒粒径和分布。