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.

The present paper reports a numerical study of a spray impinging on a surface through a crossflow. This work is intended to study the influence of the spread/splash transition criteria in the modeling of the spray impingement phenomenon. Several experimental correlations available in the literature are inserted in the same base model and the results are tested against experimental data. It can be concluded that the employment of an accurate transition criteria can improve the quality of the results.

Over the last years, there have been many investigations into new ways to obtain clean and efficient energy production. In this spirit, this study aims to successfully adapt low emission aero-engines combustors to burn biofuels. Biofuels are the immediate alternative to fossil-fuel powered aero-engines, given that by regulation is possible to apply today, a biofuel into the aeronautical industry. There are some regulations to have into account, being the biggest one the fact that the new blend must be constituted of at least 50% of conventional jet fuel (JF). In this work were selected four blends to study: 100% JF; 75% JF and 25% NEXBTL (biofuel); 50% JF and 50% NEXBTL and H2O. A smooth, dry aluminium plate was used as the impact surface and the objective was to observe the splash-deposition limits and characterize the dynamic behaviour of the droplets with and without crossflow. Different velocities of the crossflow were chosen and the impact angle of the droplet was also analysed. The splash-deposition threshold was also compared with those proposed by other authors.

Aviation education and training began early in the 20th century just after the first successful powered flight of the Wright brothers. In the present paper, the types of aviation education and training around the world are reviewed. Its developments were distinct in many different countries, and in some cases evolved from the military needs while in others from the dedication of a few enthusiasts. In the 21st century aeronautical and aerospace engineering is taught at the most advanced engineering schools in the world providing skills and competences that integrate advanced disciplines.

We study the dynamics of the rotational motion of a gyrostat satellite moving in the central Newtonian force field along a circular orbit. We propose a method for determining the equilibrium attitudes (equilibrium orientations) of a gyrostat satellite in the orbital coordinate system for given values of the gyrostatic moment vector and principal central moments of inertia, and obtain their existence conditions. For each equilibrium orientation, sufficient conditions for stability are obtained using a generalized energy integral such as a Lyapunov function. We conduct a detailed numerical analysis of domains where the stability conditions for equilibrium attitudes are satisfied depending on four dimensionless parameters of the problem. It is shown that the number of equilibrium attitudes of a gyrostat satellite for which the sufficient conditions of stability are satisfied in the general case varies from four to two with an increase in the magnitude of a gyrostatic moment. The results obtained in this paper can be used for constructing gravitational systems of control over the orientation of the Earth’s artificial satellites.

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.

The 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].

Fortunately, the human being has already started to be environmentally concerned and the search for new alternatives to reduce pollution increased. Transports are responsible for a significant portion and it is extremely necessary to bet on alternatives to oil. The introduction of biofuels in aero-engines could be an example. In order to modify and optimize piston engines and gas turbines to operate efficiently with alternative fuels, this work used Jet Fuel and Biofuel mixtures. The focus of these studies was to visualize the dynamic behavior of single droplets impinging upon liquid films with variable thickness. The existence of splash as well as its characteristics were reported and the differences and similarities between the outcomes according to the impact conditions and the fluid properties were catalogued. To achieve that an experimental facility was designed and built. Four fluids were tested: water (as reference), 100% Jet A-1, 75%/25% and 50%/50% mixtures of Jet A-1 and HVO (Hydro-processed Vegetable Oil), respectively, since civil aviation only accept mixtures with at least 50% Jet Fuel in volume. The fluid properties were measured to ensure accuracy. The liquid film depths considered were 10%, 50% and 100% of the droplet diameter. A high-speed digital camera was used to image acquisition and the droplet was released by a syringe pump connected to the needle at a specific pumping rate. The impact surface was a perspex container filled with fluid. Five needles with different inner diameters and three impact heights were employed to provide a variety of Weber and Reynolds numbers.

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.

Laser-Doppler measurements of the velocity characteristics of a ground vortex flow resulting from the collision of a wall jet with a boundary layer are analyzed using advanced statistical tools, namely finite mixtures of probability density functions. These are determined by the best fitting to experimental results using a Bayesian approach based on a Markov Chain Monte Carlo (MCMC) algorithm. This approach takes into account eventual multimodality and heterogeneities in velocity field distributions. Therefore, it provides a more complete information about heterogeneous velocity distributions and its corresponding characteristic velocities and turbulent fluctuations. The ground vortex flow investigated is generated by a wall jet-to-boundary layer velocity ratio of 2. The results evidence how finite mixtures are able to reconstruct the measured probability distribution in the form of a mathematical probability density function. This allows to improve the physical interpretation of the ground vortex flow through quantifying its complex structure, which is particularly relevant to VSTOL aircraft flows. Namely, identify the separation point oscillation region, and the enlargement of the region comprising the effect of collision between wall jet and boundary layer in planes moving away from the wall. Also, in the collision zone, following a conventional statistical analysis, the rms velocity fluctuation (u′) appears to be overestimated for the horizontal component due to the measured velocity range oscillating between positive and negative values. The results evidence how U‾ and u′ provide an idea of the flow dynamics, but their use is limited and an important amount of information associated with the highly curved flow complexity is lost. This prevents distinguish the magnitude of velocity fluctuations according to the flow direction, and the endorsement of anisotropy near the collision region, justifying the possibility of being numerically simulated.