Numerical simulation of multiphase flows under electrohydrodynamics effects
Rahmat, Amin (2017) Numerical simulation of multiphase flows under electrohydrodynamics effects. [Thesis]
Multiphase ow problems are one of the main categories of uid dynamics problems with a broad range of applications in industrial practices. Thus, it is crucial to control multiphase ow problems to maintain desirable ow regimes in those industrial applications. The electrohydrodynamics can be used to control multiphase ow problems due to its simplicity, wide range of applicability and its high precision controllability. One of possible approaches to investigate the in uence of electrohydrodynamics on multiphase ow problems is to utilize numerical methods for simulating the interaction between electric and hydrodynamic forces in complex multiphase systems. In this thesis, the numerical investigations of electrohydrodynamics e ects on multiphase ow problems are carried out by developing the Smoothed Particle Hydrodynamics (SPH) method, as well as extending a commercial Computational Fluid Dynamics (CFD) software. The simulation of multiphase ows and electrohydrodynamics is implemented by the Continuum Surface Force (CSF) and leaky dielectric models, respectively. The SPH method is a Lagrangian particle-based mesh-less method which can simulate interfacial multiphase ows with no additional computational costs. The in-house SPH code is initially validated by comparing present numerical results with those of Laplace equation for the implementation of surface tension, and with analytical solutions of Taylor and Feng theories for the deformation of a stationary droplet in the presence of electric eld. Moreover, the method is extensively validated for each of the following problems with available numerical, analytical and experimental data in literature. The rst problem is the Rayleigh-Taylor Instability (RTI) that allows performing a phenomenological study on a fundamental multiphase ow problem. The in uence of various electrohydrodynamic forces is investigated by comparing the role of Coulomb and polarization forces. Then, the method is extended to bubble rising of an oil/water system by investigating the in uence of electric forces on the deformation of a rising bubble and its rise velocity. The SPH method is also used to simulate the electro-coalescence of binary droplets. Thus, the SPH method is extended for the simulation of droplet coalescence by developing a multiphase algorithm based on the lubrication theory and lm drainage model. The algorithm is used to simulate the head-on and head-o coalescence of approaching binary droplets as well as the electro-coalescence of stationary droplets. The second approach to the simulation of multiphase ows under the electrohydrodynamic e ects is the development of a commercial CFD software, the ANSYS-Fluent. The software is extended by writing complex User De ned Functions (UDFs) for the simulation of electrohydrodynamics. In addition to the initial comparison of the numerical tool with available numerical and analytical results for the electrohydrodynamic deformation of a suspended droplet, the numerical tool is extensively validated with available data in literature for various test-cases of the following problems. The developed ANSYS-Fluent code is used to simulate the bubble rising of an air/water system for the formation of toroidal rising bubbles by investigating the combined e ects of domain con nement and electrohydrodynamics. Finally, the electro-jet printing which is an industrial scale problem is simulated for variations of di erent dimensionless parameters to provide guidelines for the design of electro-jet printing setups.
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