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Numerical Modeling of Drop Formation and Deformation using the Finite Volume Method

Sadat Salehi, Moloud | 2013

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 44383 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Firoozabadi, Bahar; Afshin, Hossein
  7. Abstract:
  8. Drop formation from the tip of a nozzle and its motion in bulk fluid is an interesting and practical process which has widely turned researchers’ attention. Investigation into the governing physics and effective parameters on formation, deformation and motion of a drop increases the efficiency of the related industrial processes. Thus in the present study, in order to simulate this process, full Navier-Stokes equations solved by the Volume of Fluid (VOF) method in an axisymmetric domain using Fluent software as the solver. In this research, the effects of Weber number (the proportion of inertial force to surface tension force) and Ohnesorge number (which refers to the proportion of viscous force to surface tension force) on the formation dynamic of drop has been studied. Results show that by increasing Weber number, the relative importance of surface tension force decreases in comparison to inertial force; consequently, drop volume and length increases whereas drop formation interval decreases. Moreover, studies show that for lower Ohnesorge number, viscous forces in the necking region decrease which reduces drop length and formation interval but the drop volume remains almost constant. Furthermore, drop deformation and transient drag coefficient for a Newtonian falling drop is also studied. In order to study the effects of deformation on drag force, results for a drop and solid sphere compared. In addition to effective parameters on a solid sphere, drop deformation and internal flows are other noticeable parameters determining drag coefficient. Actually, drag coefficient for a drop depends on Reynolds, Weber and, Ohnesorge number which in this research the effects of Weber and Ohnesorge number has been investigated. For relatively low Weber number, due to the dominance of surface tension force, deformation is negligible and drag coefficient for a solid sphere and a drop are almost the same. As the Weber number increases, deformation is more and the difference in drag coefficient between a solid sphere and a drop will be more significant. Besides, by increasing Ohnesorge number, the effect of viscous forces increases; thus, drop fluctuation amplitude decreases due to higher viscous dissipation. To sum up, by increasing Ohnesorge number pressure drag decreases whereas skin drag increases. Based on the simulation results, for pressure drag is dominant and by the increase in Ohnesorge number, overall drag coefficient decreases
  9. Keywords:
  10. Droplet Formation ; Deformation ; Transient Drag Coefficient ; Volume of Fluid ; Weber Number ; Ohnesorge Number

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