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Browsing by Issue Date, starting with "2020-01-05"

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  • 3D Simulations of Droplets Impacting Liquid Films: Crown Parameters Measurements
    Publication . Vasconcelos, Daniel; Ribeiro, Daniela; Silva, R. D.; Barata, Jorge M M
    The 3D incompressible Navier-Stokes equations are coupled with the CLSVOF method and employed to numerically simulate the phenomena of single droplet impact onto liquid films. A solution-adaptive mesh refinement tool, based on the gradient of the volume fraction scalar, is adopted in order to reduce computational cost. Three different fluids are taken into account: 100% jet fuel and 75%/25% and 50%/50% of jet fuel and biofuel, respectively. Quantitative analysis of the crown height and outer diameter is performed for different impact conditions, such as the influence of the impact velocity and dimensionless thickness, between experimental and numerical results, and the qualitative analysis includes the occurrence of splashing and overall crown evolution. Numerical results show that the crown outer diameter measurements are in good agreement with the experimental cases, presenting a slight discrepancy for the lower liquid film thickness of h*= 0.2. The crown height measurements are under-predicted for the current model, maintaining a similar trend for dimensionless thicknesses of h*= 0.5 and h*= 1 while, for the lower thickness, the crown disintegrates at earlier stages. The crown curvature and rim instabilities exhibit significant differences, and the splashing phenomenon occurs for both the experimental and numerical outcomes.
    2020-01-05Conference object Restricted access Show more
  • Morphology of Bubble Formation on Droplet Impact upon Thin Liquid Layers
    Publication . Ribeiro, Daniela; Panão, Miguel; Barata, Jorge M M; Silva, A. R. R.
    Within the wide possibilities for the resultant outcome of a single droplet impinging upon a liquid film, there is an unstudied phenomenon that seems to be underestimated or forgotten in time. The formation of a bubble by the crown sheet closure at the top after crown splash is the focus of this paper. The phenomenon was deeply studied as well as its occurrence, main features, and physical significance. It is important to understand completely the phenomenon to asses if it should be encouraged or avoided inside the combustion chamber of an IC engine, since it has higher production of secondary atomization due to the larger lifetime, and on the other hand, the bubble bursting increase the production of airborne particles that could affectthe pollutant emissions. Several impacts conditions were tested and it was found three different types of bubble formation depending on the jets formed at the closure point. The event was observed both from below and from the side, enhancing the knowledge about the droplet-film impact itself. The main features were studied including, the bubbling height and diameter, and the propagation velocity of the first perturbation imposed on the liquid film.
    2020-01-05Conference object Restricted access Show more