研究强旋来流条件横向液体射流的破碎雾化特征对先进航发燃烧室设计具有重要意义.该文采用Euler-Lagrange方法模拟了射流破碎雾化过程,基于VOF(volume of fluid)方法捕获了近场射流破碎过程中相界面的拓扑结构变化,通过Lagrange粒子追踪...研究强旋来流条件横向液体射流的破碎雾化特征对先进航发燃烧室设计具有重要意义.该文采用Euler-Lagrange方法模拟了射流破碎雾化过程,基于VOF(volume of fluid)方法捕获了近场射流破碎过程中相界面的拓扑结构变化,通过Lagrange粒子追踪(LPT)方法模化喷雾液滴的动力学过程得到远场油雾分布特征.该研究构建了不同旋流强度横向来流,旋流数从0变化至2.5,射流与气流的动量比q为10,来流We数为39.在该工况下,射流破碎过程包含柱状破碎和表面破碎.结果表明,由Kelvin-Helmholtz(KH)不稳定诱导的轴向波的发展是射流发生柱状破碎的主要原因,而射流分支/液膜从液柱表面剥离形成了射流的表面破碎,其主要由方位剪切不稳定波主导.强旋流加速了射流的柱状破碎过程,降低了破碎位置的径向高度,但旋流延迟了射流的表面破碎过程,破碎开始位置的径向高度随旋流数增大而升高.随着旋流数的增大,流向方向速度分量不断减小,射流沿径向方向的喷注轨迹显著升高;射流的偏转角度与流向位置呈线性关系,旋流数越大偏转斜率越大.此外,射流雾化场的Sauter直径(SMD)随旋流数的增加而减小,液雾场的空间分布区域也随旋流数的增加而增大.展开更多
In this study, the flow characteristics and behaviors of virgin and recycled Inconel powder for powder-bed additive manufacturing （AM） were studied using different powder characterization techniques. The results rev...In this study, the flow characteristics and behaviors of virgin and recycled Inconel powder for powder-bed additive manufacturing （AM） were studied using different powder characterization techniques. The results revealed that the particle size distribution （PSD） for the selective laser melting （SLM） process is typically in the range from 15 μm to 63 μm. The flow rate of virgin Inconel powder is around 28 s·（50 g）^-1. In addition, the packing density was found to be 60%. The rheological test results indicate that the virgin powder has reasonably good flowability compared with the recycled powder. The inter-relation between the powder characteristics is discussed herein. A propeller was successfully printed using the powder. The results suggest that Inconel powder is suitable for AM and can be a good reference for researchers who attempt to pro- duce AM powders.展开更多
Three types of nozzles: a low-pressure multistage nozzle, an effervescent nozzle and a newly developed internal- mixing air-blast nozzle, for atomization of Coal-Water Slurry (CWS) were investigated. Influence of CWS ...Three types of nozzles: a low-pressure multistage nozzle, an effervescent nozzle and a newly developed internal- mixing air-blast nozzle, for atomization of Coal-Water Slurry (CWS) were investigated. Influence of CWS properties including surface tension and apparent viscosity on atomization was studied. Comparisons among the nozzles were carried out in terms of spray droplet mean diameter and fuel output. Versatility of each nozzle was investigated and atomization mechanism of each nozzle was analyzed as well. The results showed that the newly developed internal- mixing air-blast nozzle has high fuel output and small mean droplet size in the spray, but the multistage nozzle has high versatility for handling of low quality CWS.展开更多
An experimental investigation was performed to study the heat transfer in an eight-nozzle spray cooling system with de-ionized water as the working fluid. Visualization of the liquid-solid contact area and the flow ne...An experimental investigation was performed to study the heat transfer in an eight-nozzle spray cooling system with de-ionized water as the working fluid. Visualization of the liquid-solid contact area and the flow near the heated surface was made using a microscopic lens system in conjunction with an advanced high-speed camera. The film thickness and film wavelike characteristics under liquid volume flow rates ranged from 2.78×10 -6 m 3 /s to 1.39×10 -5 m 3 /s and surface temperatures between 22℃ and 78.2℃ were examined respectively. The development process of the liquid film on the heated surface was observed. The local mean film thickness, the film wavelike characteristics and the behavior of the bubbles appeared in the liquid film were captured using an image processing technique. It is discovered that there exists a climax of local mean film thickness during the starting process of spray cooling. When the liquid film reaches the dynamic stable state, the dimensionless mean film thickness decreases with the increase of the liquid volume flow rate, and increases with the increase of surface temperature generally. Besides, the volume flow rate has a more significant impact on the wavelength and amplitude of the liquid film compared to the surface temperature.展开更多
文摘研究强旋来流条件横向液体射流的破碎雾化特征对先进航发燃烧室设计具有重要意义.该文采用Euler-Lagrange方法模拟了射流破碎雾化过程,基于VOF(volume of fluid)方法捕获了近场射流破碎过程中相界面的拓扑结构变化,通过Lagrange粒子追踪(LPT)方法模化喷雾液滴的动力学过程得到远场油雾分布特征.该研究构建了不同旋流强度横向来流,旋流数从0变化至2.5,射流与气流的动量比q为10,来流We数为39.在该工况下,射流破碎过程包含柱状破碎和表面破碎.结果表明,由Kelvin-Helmholtz(KH)不稳定诱导的轴向波的发展是射流发生柱状破碎的主要原因,而射流分支/液膜从液柱表面剥离形成了射流的表面破碎,其主要由方位剪切不稳定波主导.强旋流加速了射流的柱状破碎过程,降低了破碎位置的径向高度,但旋流延迟了射流的表面破碎过程,破碎开始位置的径向高度随旋流数增大而升高.随着旋流数的增大,流向方向速度分量不断减小,射流沿径向方向的喷注轨迹显著升高;射流的偏转角度与流向位置呈线性关系,旋流数越大偏转斜率越大.此外,射流雾化场的Sauter直径(SMD)随旋流数的增加而减小,液雾场的空间分布区域也随旋流数的增加而增大.
基金financial support provided by A*STAR Additive Manufacturing Centre (AMC) Initiative: Work package 1-High temperature materials development for 3D additive manufacturing (142680088)
文摘In this study, the flow characteristics and behaviors of virgin and recycled Inconel powder for powder-bed additive manufacturing （AM） were studied using different powder characterization techniques. The results revealed that the particle size distribution （PSD） for the selective laser melting （SLM） process is typically in the range from 15 μm to 63 μm. The flow rate of virgin Inconel powder is around 28 s·（50 g）^-1. In addition, the packing density was found to be 60%. The rheological test results indicate that the virgin powder has reasonably good flowability compared with the recycled powder. The inter-relation between the powder characteristics is discussed herein. A propeller was successfully printed using the powder. The results suggest that Inconel powder is suitable for AM and can be a good reference for researchers who attempt to pro- duce AM powders.
文摘Three types of nozzles: a low-pressure multistage nozzle, an effervescent nozzle and a newly developed internal- mixing air-blast nozzle, for atomization of Coal-Water Slurry (CWS) were investigated. Influence of CWS properties including surface tension and apparent viscosity on atomization was studied. Comparisons among the nozzles were carried out in terms of spray droplet mean diameter and fuel output. Versatility of each nozzle was investigated and atomization mechanism of each nozzle was analyzed as well. The results showed that the newly developed internal- mixing air-blast nozzle has high fuel output and small mean droplet size in the spray, but the multistage nozzle has high versatility for handling of low quality CWS.
基金supported by the National Natural Science Foundation of China under Grant No.50906083National Basic Research Program of China under Grant No.2011CB710705
文摘An experimental investigation was performed to study the heat transfer in an eight-nozzle spray cooling system with de-ionized water as the working fluid. Visualization of the liquid-solid contact area and the flow near the heated surface was made using a microscopic lens system in conjunction with an advanced high-speed camera. The film thickness and film wavelike characteristics under liquid volume flow rates ranged from 2.78×10 -6 m 3 /s to 1.39×10 -5 m 3 /s and surface temperatures between 22℃ and 78.2℃ were examined respectively. The development process of the liquid film on the heated surface was observed. The local mean film thickness, the film wavelike characteristics and the behavior of the bubbles appeared in the liquid film were captured using an image processing technique. It is discovered that there exists a climax of local mean film thickness during the starting process of spray cooling. When the liquid film reaches the dynamic stable state, the dimensionless mean film thickness decreases with the increase of the liquid volume flow rate, and increases with the increase of surface temperature generally. Besides, the volume flow rate has a more significant impact on the wavelength and amplitude of the liquid film compared to the surface temperature.
