Breakup and Atomization Characteristics of Liquid Jets in Strong Swirling Crossflow Based on the VOF-LPT Method
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摘要: 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.Abstract: The liquid jet breakup and atomization interacting with a strong swirling crossflow is of significance in designing advanced aeroengines. The Eulerian-Lagrangian method was utilized to simulate the jet breakup and atomization processes. The volume of fluid (VOF) method was employed to track the gas-liquid interface topology evolution during the jet breakup, while the Lagrangian particle tracing (LPT) method was used to track the discrete droplets and obtain the information on far-field liquid dispersion. The crossflow was designed with different swirl numbers, ranging from 0 to 2.5. Momentum ratio q between the liquid jet and the air flow was set to 10, and the gas Weber number was 39. Under these conditions, both the column and shear breakups were observed. The results indicate that, the development of axial waves induced by the Kevin-Helmholtz (KH) instability was the main cause for column breakup. During the surface breakup, ligaments and small liquid jet branches were stripped from the liquid jet surface, primarily driven by azimuthal shear waves. The strong swirling airflow enhances the jet column breakup process, leading to a lower radial height for the breakup location and a shorter breakup time. However, as the swirl number increases, the radial height of the onset of breakup would increase, which suggests the swirl flow would delay the surface breakup of liquid jets. With the increase of the swirl number, the velocity component in the flow direction decreases, and the jet trajectory in the radial direction increases significantly. The deflection angle of the jet shows a linear relationship with the position of the flow direction, with larger air swirl numbers resulting in a steeper slope. Furthermore, as the swirl number increases, the Sauter mean diameter (SMD) of the entire spray field would decrease, and the liquid dispersion would increase.
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Key words:
- swirling crossflow /
- liquid jet /
- VOF /
- LPT /
- breakup and atomization characteristic
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图 1 旋流射流相互作用计算模型
Figure 1. Illustration of the computation setup for the swirl-jet interaction
图 2 旋流数为0的迎风面喷注轨迹结果与实验结果比较
Figure 2. Comparison of the windward trajectory with the experimental results for Ns=0
图 3 旋流数为0时液滴粒径随径向高度变化以及与实验结果的比较
注 为了解释图中的颜色，读者可以参考本文的电子网页版本，后同.
Figure 3. Droplet sizes varying with the radial height compared with the experimental results for Ns=0
图 4 旋流与射流相互作用喷雾结构
Figure 4. The spray structure of the interaction between swirls and jets
图 5 不同旋流数条件下破碎开始位置以及破碎位置的径向高度
Figure 5. Radial heights of the breakup onset and the breakup location for different swirl numbers
图 6 旋流与射流相互作用喷雾结构三视图(a)—(c)及射流近场破碎结构(d)
Figure 6. Three views of spray structures (a)—(c) and the near-field break-up structure of swirling jet interaction (d)
图 7 Case 0—case 3射流近场时间演化结果
Figure 7. Time resolved near-field liquid jets in case 0—case 3
图 8 柱坐标系下case 1的喷注轨迹与喷雾平均场结果
Figure 8. The injection trajectory and the spray mean field results of case 1 in the cylindrical coordinates
图 9 不同旋流数下喷注轨迹比较
Figure 9. Comparison of injection trajectories under different swirling numbers
图 10 不同旋流数下偏转角度结果
Figure 10. Deflection angle results under different swirling numbers
图 11 Case 0—case 3在x/d=10处平面液滴空间分布
Figure 11. Spatial distributions of planar droplets at x/d=10 in case 0—case 3
图 12 Case 1不同轴向距离平面液滴空间分布
Figure 12. Spatial distributions of planar droplets with different axial distances in case 1
A1 Case 2的xOz平面(a)和xOr平面(b)喷雾平均结果比较
A1. Average sprays of xOz plane(a) and xOr plane(b) in case 2
A2 Case 2有无坐标变化得到的喷注轨迹比较
A2. Comparison of the trajectories for the xOz plane and the xOr palne
A3 柱坐标系下case 1的xOθ平面偏转角度提取与喷雾平均场结果
A3. Average spray results along the xOθ plane and the deflection angle extraction in case 1
表 1 射流液体以及来流气体物理性质
Table 1. Liquid and gas properties
parameter value gas density ρg/(kg/m3) 1.25 gas viscosity μg/(m2/s) 1.46E-5 liquid density ρl/(kg/m3) 997 liquid viscosity μl/(m2/s) 1.01E-6 surface tension coefficient σ/(N/m) 0.071 
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表 2 不同旋流数下空气来流与射流的工况设置
Table 2. Numerical setups for different swirling numbers
cases Ns Ug/(m/s) u/(m/s) v/(m/s) Ul/(m/s) case 0 0 74 74.00 0.00 8.29 case 1 0.5 74 68.62 27.71 8.29 case 2 1 74 57.57 46.50 8.29 case 3 2.5 74 32.84 66.31 8.29
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表 3 不同旋流度下射流SMD结果
Table 3. Jet SMD results under different swirling numbers
cases Ns dSMD/μm case 0 0 60.80 case 1 0.5 52.66 case 2 1 48.94 case 3 2.5 48.15
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表 4 不同位置截面射流SMD结果
Table 4. Jet SMD results at different cross sections
cases x/d=10 x/d=20 x/d=30 x/d=40 dSMD case 0 55.21 60.75 64.91 59.34 60.80 case 1 49.02 55.26 54.94 51.75 52.66 case 2 49.29 49.06 49.49 46.06 48.94 case 3 50.03 47.94 46.56 45.03 48.15
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