Imaging and Numerical Simulation of Unsteady Spray

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An unsteady spray is composed of ten millions of droplets. Their minute behavior affects the combustion process of the spray. Consequently, it is very useful for understanding the process to capture their spatial distribution. However, the spatial resolution of photographs taken by CCD camera is very low and it is difficult to recognize the individual droplet when the whole spray is taken on a photograph and only the local information is captured by the enlarged photography. The unsteady spray itself has the three dimensional structure, nevertheless, there is very little research to find this kind of structure. This project proposed the new technique of the super enlarged photography and calculated the two and three dimensional structures of an unsteady spray by the numerical simulation.The system of the super enlarged photography was composed of the lens system like a telescope of refraction type and a laser with low coherency and a large sized film (8[m] x 10[in]). It was able to cat … More ch the droplets information out of the region near the spray axis where the droplets density is too much through this optics and to obtain the two dimensional structure of the unsteady spray applying PIV technique to a photograph. Before about 35 years ago the head investigator found the droplets information in the range of about only 2[mm] from the spray envelope which was taken on a 35[mm] film by use of enlarging photography with a telescope.The numerical simulation was carried out by applying DDM for droplets and LES for the gaseous turbulence under the reference of KIVA code. It was capable of simulating the two dimensional structure of the spray by increase in the number of numerical mesh, by decrease in the numerical viscosity through the application of CIP technique and by optimization of breakup model And it is possible to calculate the two dimensional structure of vortex by LIC and the three dimensional structure of vortex by velocity gradient tensor.The main conclusions are as follows :1. It is able to capture the droplets information in the range from about 3[mm] from the spray axis to the spray envelope by use of new optics proposed.2. The Sauter mean diameter of droplets is ranged about from 10[μm] to 20[μm]. It decreases as the injection pressure increases.3. The droplets with small and medium size follow the movement of vortex with large scale generates at the spray tip region and those with large size appear at the outside of the vortex. The two dimensional arrangement of vortices is alternately and the three dimensional one is the multiplex of the vortices like hairpin. Less