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Detailed numerical study of primary atomization of a liquid jet in swirling crossflow
Liquid jets in cross flow find wide applications in engineering fields, especially in the aerospace domain – combustors of gas
turbine engines. This study involved Volume-Of-Fluid based numerical simulations of a liquid jet injected into gas-crossflow
in swirling motion. The liquid is injected radially outwards from a central tube to a confined annular space with gas crossflow.
Simulations are conducted at high liquid-to-gas density ratio (Dr) of 180:1 and different liquid-to-gas momentum ratios (Q) upto
25. The Swirl Number (SN) of the gas crossflow was varied between 0 and 0.84. The liquid jet undergoes column and shear modes
of breakup as observed in experimental studies. Spray characteristics such as drop size distribution, velocity of the drops, shape
factor and column breakup length were analysed. Simulations effectively capture the influence of swirl flow on the spray characteristics.
This project was carried out under the guidance of Prof. Gaurav Tomar and was supported by Pratt and Whitney, USA.
No swirl case.
Swirl case with Swirl Number = 0.84.
Density ratio and Reynolds number effect in the secondary breakup of drops at moderate Weber numbers
Breakup of drops is ubiquitous in nature. In the present study, fully resolved Volume of Fluid (VOF) simulations are performed to understand the physics involved in the breakup of a single initially spherical droplet in a gas flow. Most of the previous numerical studies involve investigation of the breakup of drops at low-density ratios (drop liquid to ambient fluid ratio rho* < 100). It has been observed that the backward bag breakup is the predominant mode in this density ratio range at moderate Weber numbers (20-80). Whereas, in our previous study Jain et al. (2015), we observed a forward-bag breakup at a density ratio of 1000 for moderate Weber numbers as also seen in experiments. Hence in the current work, we study the breakup for wide range of density ratios (rho*=10-1000) to understand this dependence of characteristics of breakup such as the dynamics of drop deformation, drop morphology and breakup modes on the density ratio, rho*. We found that there exists a density ratio (rho*~150) above which the characteristics of breakup are same and are significantly different from that for low density ratios. We use scaling analyses to explain these characteristics of the drop breakup. We also study the role of the dynamics of the droplet rim and the Rayleigh-Taylor instability, at different density ratios in the bag formation process. In addition, we studied the effect of gas Reynolds number, Re_g at different viscosity ratios, M and in turn the effect of Oh_l on the breakup of drops and found that the $Oh_l$ has an effect on breakup even for the values, Oh_l<0.1. Finally, we present a rho*-We phase plot reflecting the drop behavior at various density ratios and Weber numbers.
Density ratio = 10, Weber number = 20.
Density ratio = 1000, Weber number = 20.