Browsing by Issue Date, starting with "2019-01-06"
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- Aerodynamic Breakup of a Single Droplet due to a Crossflowed AirstreamPublication . Carrolo, Gabriel Alexandre da Costa; Ribeiro, Daniela; Barata, Jorge M M; Silva, A. R. R.The main breakup regimes are visualized and studied with the help of a high-speed camera and a continuous jet of air, provided by a wind tunnel, is used to transition the droplet into the various stages of secondary atomization. The use of Jet Fuel and Biofuel mixtures is the focal point of this study. All the known regimes are encountered and each transitional We is calculated. The variation of We due to Oh is described, in addition to the comparison between We number thresholds and correlations existent in the literature for each regime transition. The influence of these numbers on the dimensionless characterization of time and later the maximum cross stream diameter is shown. Finally, a correlation for the temporal evolution of the drops’ cross stream diameter for all regimes, assuming its deformation is not a linear function of time, is proposed.
- Numerical Modeling of a Cooling Water Droplet Using a Two-Phase Flow ApproachPublication . Franco, André; Barata, Jorge M M; Silva, A. R. R.The study and understanding of cooling and freezing water droplets is of paramount importance due to their influence in the decrease of aerodynamic performance on lifting surfaces. It is imperative to develop models capable of simulating the freezing processes and ice accretion effects, in order to predict with maximum efficiency freezing and avoid this phenomenon or even taking advantage of it and develop new technologies that ultimately will improve air travel. As such, this paper aims to study the cooling of a water droplet in free fall. A two-way coupling model is implemented to evaluate the influence of gas-drop and drop-gas interactions, numerically investigating the cooling of free falling droplets for different diameters and air humidity ratios. The predictions are compared with experimental and numerical data with the objective of providing insight into the degree of heat and mass transfer involved. Some correlations to account for the convection effects are introduced and are found to be in close agreement with the experimental data.
- Precision Sextant: An Early Portuguese Landmark on Aeronautical HistoryPublication . Neves, Fernando M. S. P.; Silva, A. R. R.; Barata, Jorge M MThe Transatlantic Flights performed at 1919 proved to be a tremendous success; however, aerial navigation over ocean was based on radio equipment. Sextants were very difficult to use, and methods of calculations were quite time-consuming to provide positioning results of an aircraft at great speeds. For these reasons, the Aerial Astronavigation was considered unsuitable. 3 years later, two Portuguese airmen managed to perform the First Aerial Crossing of the South Atlantic exclusively achieved by Aerial Astronavigation in an unprecedent route precision achievement; such feat was a milestone in Aviation History, marking the debut of the sextant as a key mean for air navigation: for the first time, sextant, course corrector and methods of calculations proved their effectiveness and value for aerial navigation. Reports of the 1st South Atlantic Air Crossing [Relatórios da 1ª Travessia Aérea do Atlântico Sul] written by Coutinho and Cabral, published in 1922, were included in the International Register of the “Memory of the World” of UNESCO. After July 27, 2011, the reports were considered World Heritage [Património da Humanidade].
- Comparative Study of Droplet Impact onto Sloped Surface versus a Droplet Impact onto a Surface with a CrossflowPublication . Ferrão, Inês Alexandra dos Santos ; Ribeiro, Daniela; Barata, Jorge M M; Silva, A. R. R.Droplet impact is a common phenomenon that occurs frequently in several applications such as fuel injection in internal combustion engines, processes involving spray paints and cooling of electronic equipment. In the study of droplet impingement, the influencing parameters are the liquid, along with its physical properties, the impact surface, the surrounding environment and others conditions. The major goal of the present work is a comparison that involves an experimental study of the phenomena occurring during the impact of liquid droplets onto a dry surface with a cross flowing air and droplets impacting onto a sloped surface. Due to the crossflow, the droplet does not have the same direction as the gravitational acceleration and suffers a certain deformation that seems to vary the impact condition. For the sloped surface, the droplet is spherical throughout the trajectory and both the gravitational acceleration and movement of the droplet have the same direction. Four fluids were used: 100% Jet-Fuel, 75% Jet-Fuel-25% HVO, 50% Jet-Fuel-50%. HVO and H2O (pure water) as a reference. In order to maintain the coherence of the results between the two experimental works, the impact velocity and incident angle were kept approximately the same.