Numerical study of electric Reynolds number on electrohydrodynamic (EHD) assisted atomization
Sheehy, Patrick John Harper
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In today's modern world, nearly all industries utilize the benefits of fast, long distance transportation that burning fossil fuels deliver. However, fluctuating fuel prices has created interest in researching alternatives to fossil fuels. Bio-fuels are one of these alternatives, but they generally have a higher viscosity and water content than diesel. This means high pressures are required to atomize the fuel in the combustion chamber, thus bio-fuels are limited to larger or less efficient engines. A potential method to reduce the pressure requirements is to use Electrohydrodynamic (EHD) assisted atomization. EHD assisted atomization injects electrical charges into the liquid fuel before spraying, meaning the fuel has an electrical charge distribution before and after atomization. For many relevant engineering flows, including liquid fuel injection, the charge mobility timescale (time it takes the charges to relax to the fluid-gas boundary) is similar in magnitude to the charge convection timescale (relevant flow time), which leads to a non-trivial electric charge distribution. This distribution within the liquid fuel may enhance atomization, the extent to which is dependent on the ratios of the timescales which are known as the electric Reynolds number (Re subscript e). In this work, a computational approach for simulating two-phase EHD flows is used to investigate the amount Re subscript e influences the resulting atomization quality. The computational approach is second-order, conservative, and is used to consistently transport the phase interface along with the discontinuous electric charge density and momentum. The scheme sharply handles the discontinuous electric charge density, allowing robust and accurate simulations. In addition, this method is modified by a work distribution scheme to improve processor utilization on High Performance Computing (HPC) clusters. Using these methods, multiple three-dimensional test cases are simulated with varying Re subscript e values which highlight the effect of Re subscript e on the atomization efficiency of a liquid jet. Comparison of these cases shows the importance of Re subscript e on atomization and suggests that decreasing Re subscript e (increasing charge mobility) leads to larger concentrations of electric charge density, increased Coulomb force, and ultimately improved break-up during the atomization process.