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Numerical Simulation on Head-On Binary Collision of Gel Propellant Droplets
College of Aerospace Science and Engineering, National University of Defense Technology, 109 Deya Road, Changsha 410073, China
* Author to whom correspondence should be addressed.
Received: 15 November 2012; in revised form: 25 December 2012 / Accepted: 26 December 2012 / Published: 8 January 2013
Abstract: Binary collision of droplets is a fundamental form of droplet interaction in the spraying flow field. In order to reveal the central collision mechanism of two gel droplets with equal diameters, an axi-symmetric form of the Navier-Stokes equations are firstly solved and the method of VOF (volume of fluid) is utilized to track the evolution of the gas-liquid free interface. Then, the numerical computation model is validated with Qian’s experimental results on Newtonian liquids. Phenomena of rebound, coalescence and reflexive separation of droplets after collision are investigated, and structures of the complicated flow fields during the collision process are also analyzed in detail. Results show that the maximum shear rate will appear at the point where the flow is redirected and accelerated. Rebound of droplets is determined by the Weber number and viscosity of the fluid together. It can be concluded that the gel droplets are easier to rebound in comparison with the base fluid droplets. The results also show that the alternant appearance along with the deformation of droplets in the radial and axial direction is the main characteristic of the droplet coalescence process, and the deformation amplitude attenuates gradually. Moreover, the reflexive separation process of droplets can be divided into three distinctive stages including the radial expansion, the recovery of the spherical shape, and the axial extension and reflexive separation. The variation trend of the kinetic energy is opposite to that of the surface energy. The maximum deformation of droplets appears in the radial expansion stage; in the case of a low Weber number, the minimum central thickness of a droplet appears later than its maximum deformation, however, this result is on the contrary in the case of a high Weber number.
Keywords: gel propellant; droplet head-on collision; VOF method; numerical simulation
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Liu, Z.; Wu, J.; Zhen, H.; Hu, X. Numerical Simulation on Head-On Binary Collision of Gel Propellant Droplets. Energies 2013, 6, 204-219.
Liu Z, Wu J, Zhen H, Hu X. Numerical Simulation on Head-On Binary Collision of Gel Propellant Droplets. Energies. 2013; 6(1):204-219.
Liu, Zejun; Wu, Jianjun; Zhen, He; Hu, Xiaoping. 2013. "Numerical Simulation on Head-On Binary Collision of Gel Propellant Droplets." Energies 6, no. 1: 204-219.