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- On the use of finite mixtures to improve the physical interpretation of a ground vortex flowPublication . Silva, A. R. R.; Panão, Miguel; Barata, Jorge M MLaser-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.
- Numerical Simulation of Twin Impinging Jets in Tandem Through a CrossflowPublication . Vieira, Diana; Barata, Jorge M M; Neves, Fernando M. S. P.; Silva, A. R. R.The flow field of ground vortex generated by twin impinging jets in tandem through a crossflow is numerically studied in detail. Numerical simulation and visualization are presented for two turbulent circular jets emerging into a low velocity cross stream, impinging after on a flat surface perpendicular to the geometrical jet nozzle axis. The numerical study is based in experimental studies done early, so all the features of the experimental flow were maintained when the numerical simulation was performed. The Reynolds number used was based on the jet exit conditions of 43.000-105.000, a jet to crossflow velocity ratio of 22.5-43.8 an impinging height of 20.1 jet diameters and an interject spacing’s of S = 5D and L = 6D. The analysis of the flow was extended to regions and flow conditions for which no measurements have been obtained in last experimental studies, i.e., for velocity ratios of 7.5-60. The numerical results show that for the smallest velocity ratios the jets initially do not mix but remain together in two layers. Three different types of flow regimes were identify, therefore when VSTOL aircrafts operating in ground vicinity, only the regime with strong impingement on ground and with a formation of a ground vortex is relevant. The numerical results allowed to extend the last experimental studies and prove that the deflection of the rear jet is due to the competing influences the wake, the shear layer, the downstream wall jet of the first jet and the crossflow.
- Collision Dynamics of a Single Droplet onto a Heated Dry Surface: Jet Fuel and HVO MixturesPublication . Pinto, Pedro Miguel Moreira; Vasconcelos, Daniel; Ribeiro, Daniela; Barata, Jorge M M; Silva, AndréUnderstanding the phenomena behind droplet impact is essential to improve the effectivenessin many industrial applications, such as fuel injection in an internal combustion engine andrapid spray cooling of hot surfaces. This study focuses on an experimental investigation ondroplet impact onto a heated wall. The purpose of this work is to analyse the influence of walltemperature on the morphology of a single droplet impact and observe the possible outcomes.In these experiments, the observation of all heat regimes was possible. Since there is an urgeto implement biofuels in general aviation, the fluids analysed are fuel based. The fluids usedwere distilled water, as a control group, 100% jet fuel, and a mixture of 50% biofuel with 50%jet fuel. This mixture corresponds to the maximum of renewable energy source fuel due to theminimum of 50% of jet fuel required by civil aviation. The impact energy was kept constant, andthe Weber number was set to 320. Furthermore, different wall temperatures were chosen (25◦C−320◦C) to seek every possible impact phenomenon and characterise the impact morphology.The impact dynamics were captured using a high-speed digital camera and the images weredigitally processed.
- Pressure Based Comparison of Different Gas Turbine Ground Vortex FlowsPublication . Barata, Jorge M M; Manquinho, Pedro; Silva, AndréThe present paper has the previous work of Barata et al in mind and has the purpose of analyzing the behavior of ground vortex flows through several values of height of the engine axis above the ground, diameter of engine intake and inlet airflow velocity using pressure on the ground and in a 3D scale for that.
- Sacadura Cabral and the Dawn of Portuguese AviationPublication . Neves, Fernando M. S. P.; Barata, Jorge M M; Silva, AndréSacadura Cabral was one of the two Portuguese navigators that crossed by air the South Atlantic in the beginning of the 20th century. From 1901 to 1915 Sacadura was at Mozambique and Angola where he developed geodetic and geographical missions of the greatest importance for Portuguese interest at Africa. With the Great World War requirements as a Navy Officer with 34 years old he decided to serve Portugal at the Aviation. In 1915 he went to France and obtained its pilot license. In 1916 Sacadura returned to Portugal and begun its instructor pilot career. He developed the “path corrector” which he created to compensate the drift caused by wind. In 1922 Sacadura made the First Air cross from Europe to South Atlantic. In 1923 he proposes himself to make an attempt to the First Air Circumnavigation Journey. He developed all its possible efforts to initiate this journey in March of 1924; however some delays had forced him to postpone the journey. Sacadura received important official medals and prizes, including the PhD Honoris Causa from the Universities of Lisbon and Oporto. In 1924 he died before he could carry out its Circumnavigation Air Journey.
- The First Aerial Raid From Portugal to MacauPublication . Neves, Fernando M. S. P.; Barata, Jorge M M; Silva, AndréIn 1920, Brito Pais and Sarmento de Beires tried an unsuccessful flight attempt from Amadora, Lisbon to Madeira Island aboard the airplane Breguet XIV A2, named "Cavaleiro Negro". Despite the scarce means of navigation they reach Madeira, which failed to land due to dense fog. On the way back after 8 hours of flight time, they alight at the Atlantic Ocean for lack of fuel and were rescued at about 500 km from Lisbon. In 1922, Gago Coutinho and Sacadura Cabral conducted the First Aerial Cross of the South Atlantic, flying from Lisbon to Rio de Janeiro. The Portuguese Aeronautics rejoiced auspicious days that time, with its aviation pioneers trying consecutively to reach more distant places along intercontinental flights. In 1923 Gago Coutinho and Sacadura Cabral were contemplating to perform an Around the World Flight. However, Sacadura died in 1924, while piloting an airplane acquired for the circumnavigation voyage. Also in 1924 the pilots Brito Pais and Sarmento de Beires idealized the conducting of a trip to Macau as an aspiration for a future Portuguese Around the World Flight attempt. On 7 April 1924, those pilots departed from Vila Nova de Milfontes in a Breguet XVI Bn2 airplane, beginning a trip to Macau. On 7 May an engine failure forced them to crash in India. On 30 May they managed to continue the Voyage in a De Havilland DH9 aircraft before being forced to end their attempt in 20 June in flying over Macau. A typhoon hindered their efforts to land and the airplane was crash landed in Chinese Territory about 800 meters from the Hong Kong Border. On 25 June 1924, they were shuttled back to Macau by boat. Brito Pais, Sarmento de Beires and Manuel Gouveia returned to Portugal, via North America, visiting several Portugueses nuclei at China, Japan, United States and England. They went to Portugal on 9 September, after having flown a total of 16760 kilometers in 117: 41h facing often extremely adverse atmospheric conditions, sandstorms and inaccurate navigation maps.
- Liquid film dynamic on the spray impingement modelingPublication . Rodrigues, Christian; Barata, Jorge M M; Silva, AndréThe present paper addresses a liquid film submodel included into a computational model that aims at reproducing the spray impingement phenomena. This numerical extension incorporates the spread of the liquid film over the neighboring nodes due to the dynamic motion induced by the film inertia and also the exchange of mass between the liquid layer and the incident and splashing particles. Moreover, a dimensionless film thickness parameter is embedded in the submodel by mean of an experimentally deduced correlation that can be fitted and updated to specified conditions. In order to realize how the model behaves with different influencing parameters, a thorough investigation is performed: the results that are obtained with and without the inclusion of the liquid film submodel are compared against the experimental data for two crossflow velocities. The integration of the computational extension with the spread/splash transition criterion is also evaluated by considering two types of expressions: one that includes the effect of the film thickness and one that does not. The results show that the latter option combined with the submodel does not distinctly enhance the simulation results, contrary to what happens with the transition criterion that considers the film thickness as an influencing parameter. In this case, the model with the computational extension reveals better prediction results, which indicates the necessity of considering it for spray impingement simulations along with a splash threshold that depends on the liquid layer.
- Twenty-Five Years of Portuguese Aviation Events at AmadoraPublication . Neves, Fernando M. S. P.; Barata, Jorge M M; Silva, A. R. R.From 1912 to 1938, the Amadora became the central location for several of Portugal's most significant aviation events. After a Kite-Flying Competition (1912), Flying Demonstrations (1913), and the 1st Air Festival in Portugal (1917), in 1919, the village became selected to host the Military Aviation Squadron GEAR - Grupo de Esquadrilhas de Aviação «República.» As WWI ended, Aviation shifted its vision to new dimensions of international civil transport. With their minds set on developing Portuguese Civil Aviation, the GEAR pilots started using military aircraft for civilian flight purposes. Thus, between 1920 and 1936, memorable and significant flights departed from Amadora to the most varied Portuguese territories worldwide; 1) Amadora – Madeira Flight Attempt (1920); 2) First Aerial Raid from Portugal to Macau (1924); 3) Amadora – Guinea (1925); 4) A Trailblazing Flight for Portuguese Overseas Commercial Air Route (1928); 5) Amadora – Portuguese India (1930); 6) Round trip Flight Amadora – Guinea – Angola (1930/31); 7) Aerial Journey from Portugal to East Timor, Macau, India, and Return (1934); and 8) Portuguese Empire Mission Amadora – Angola – Mozambique (1935/36). Furthermore, in 1934 and 1935, Amadora received the two firsts International Air Festivals in Portugal. Finally, after nearly Twenty-Five Years of Portuguese Aviation Events in Amadora, Military Aeronautics ended Amadora's connection to national aviation in 1938, thus dictating the end of the Portuguese Pioneer Flights. Organizational reasons, in addition to the smallness and deficiencies of the dirt runway track, determined the extinction of the Grupo de Aviação de Informação n.º 1 [as the GEAR was renamed], whose personnel and material would be later transferred to Tancos.
- On the Modeling of a Spray Impingement Onto a Hot SurfacePublication . Silva, A. R. R.; Rodrigues, Christian; Barata, Jorge M MThe present investigation addresses the impingement of a spray onto a heated solid surface under crossflow conditions at low pressure injection - typical of port-injection engines - during cold start. The characteristics of the initial spray are established by employing an empirical procedure, which relies on a comprehensive set of free spray measurements. This computational study considers the presence of a crossflow moving perpendicularly to an interposed surface and the formation of a dynamic liquid film over the impingement wall. Both previous conditions are often neglected in numerical simulations, despite their importance on the final outcome. Distinct wall and crossflow temperatures are analyzed systematically to evaluate the influence of droplets evaporation on the final outcome of spray impingement, and, particularly, on the distribution of the thin liquid film over the surface. The present computational model already proved to deliver accurate predictions of the spray/wall interactions under different conditions. In this work, the conditions are extrapolated to a heated environment, which reproduce more adequately what is found in in-cylinder situations. The computational model is adapted to meet the new requirements and perform within the range of conditions for which it is now formulated. The analysis shows that higher temperatures lead to smaller impinging droplets, an increase in the number of depositing droplets but a decrease in the fraction of mass of particles contributing to the liquid film; and a more uniform distribution of the liquid layer over the surface.
- Computational study on coaxial nitrogen-hydrogen injection at supercritical conditionsPublication . Magalhães, Leandro; Silva, André; Barata, Jorge M MIn the present work, we perform a computational study on the mixing of nitrogen and hydrogen at supercritical conditions. A coaxial injection configuration is considered where nitrogen is injected through the central post with a hydrogen co-flow. The flow in both injectors as well as in the combustion chamber is considered in the computations. This preliminary version presents the radial density profiles maximum of both species and radial density profiles at selected locations.