- Universidade da Beira Interior, Aeronautical Engineering, Faculty Memberadd
Copyright © 2019 by Inês A. S. Ferrão; Daniela F. S. Ribeiro; Jorge M. M. Barata; André R. R. Silva. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission.Droplet impact is a common phenomenon that... more
Copyright © 2019 by Inês A. S. Ferrão; Daniela F. S. Ribeiro; Jorge M. M. Barata; André R. R. Silva. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission.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.The present work was performed for the interinstitutional project “BISI – Biofuel Spray Impact in Aero-Engines” under the scope of Laboratório Associado em Energia, Transportes e Aeronáutica (LAETA) – activities and it was supported by Fundação para a Ciência e Tecnologia (FCT) through the project UID/EMS/50022/2013, and by Fundação Luso-Americana para o Desenvolvimento (FLAD) through the project 07/2019. Fundação Luso-Americana para o Desenvolvimento (FLAD) Project 07/2019.info:eu-repo/semantics/publishedVersio
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Fundacao para a Ciencia e a Tecnologia (FCT) e Fundacao Luso-Americana para o Desenvolvimento (FLAD) Proj. no 05/2020
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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... more
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.info:eu-repo/semantics/publishedVersio
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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... more
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].info:eu-repo/semantics/publishedVersio
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Copyright © 2019 by Gabriel A. C. Carrolo; Daniela F. S. Ribeiro; Jorge M. M. Barata; Andre R. R. Silva. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission.
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Copyright © 2017 by Jorge M. M. Barata, André R. R. Silva and Diana F. C. Vieira. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission. AIAA SciTech ForumThe complex flow field generated by the impact... more
Copyright © 2017 by Jorge M. M. Barata, André R. R. Silva and Diana F. C. Vieira. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission. AIAA SciTech ForumThe complex flow field generated by the impact of twin impinging jets in tandem through a low velocity crossflow was numerically studied. The Reynolds number based on the jet exit conditions was 43,000, the jet-to-crossflow velocity ratio from 7.5 to 90, and an interject spacing of 6 diameters of the jet. The impingement heights used were 3 to 15. The mathematical model used is based on the solution of the continuity and momentum equations. A RANS formulation was adopted with the “k-ε” turbulent model to represent the turbulent stresses. The numerical results showed the influence of the impingement height on the ground vortex location, size and interaction with the surrounding flow, but new aspects of this type of flows were found for the present case of a tandem configuration. In the region between the jets the usual fountain upwash flow does not occur, but a second small ground vortex was detected for H/D≤10, due to the interaction between the wall jets of each impinging jet. To our knowledge this is a new phenomenon that is being reported in the literature for the very first time.info:eu-repo/semantics/publishedVersio
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Copyright © 2017 by Jorge M. M. Barata, Telmo J. A. Silva, Fernando M. S. P. Neves and Andre R. R. Silva. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission.
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Copyright © 2017 by André R R Silva, Christian M G Rodrigues, Jorge M M Barata. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission.Spray impingement is an important phenomenon affecting a wide... more
Copyright © 2017 by André R R Silva, Christian M G Rodrigues, Jorge M M Barata. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission.Spray impingement is an important phenomenon affecting a wide variety of applications. The present work describes the developments that our research group that have been made to a basic spray impingement model to account for the influence of several parameters, such the liquid film deposited onto the surface, the wall temperature or the crossflow velocity. Numerical simulations are carried out for predicting the outcome of such flows that include liquid film formation, the droplet breakup and the spray evaporation. An empirical procedure is used to define the initial spray characteristics, which relies on a comprehensive set of free spray measurements. The computer model is evaluated by comparing the numerical simulations against experiments on spray impacting on a solid surface with the presence of a crossflow. The predicted results show a reasonable agreement with the measurements. Moreover, further results are presented on the formation droplets due to the deformation and breakup mechanisms.The present work has been performed under the scope of the LAETA - Laboratorio Associado em Energia, Transportes e Aeronautica - activities. C. R. thanks the Fundacao para a Ciencia e Tecnologia (FCT) for the financial support throught the PhD grant SFRH/BD/77651/2011. A. S. thanks the Fundacao Luso-Americana para o Desenvolvimento (FLAD) for the financial support throught the Proj. 1/2017. Fundação Luso-Americana para o Desenvolvimento Proj. 1/2017info:eu-repo/semantics/publishedVersio
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Flow visualization results are presented for a highly curved flow resulting from the collision of plane turbulent wall jet with a boundary layer. This configuration can be found in the case of impinging jets of a V/STOL aircraft operating... more
Flow visualization results are presented for a highly curved flow resulting from the collision of plane turbulent wall jet with a boundary layer. This configuration can be found in the case of impinging jets of a V/STOL aircraft operating in ground vicinity. The experiments were carried out for wall jet to boundary layer velocity ratio of 1.57. The present results revealed the existence of two small vortexes located in the collision zone, that exhibit an unsteady behaviour.
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In Liquid Rocket Engines, higher combustion efficiencies come at the cost of the propellants exceeding their critical point conditions and entering the supercritical domain. The term fluid is used because, under these conditions, there is... more
In Liquid Rocket Engines, higher combustion efficiencies come at the cost of the propellants exceeding their critical point conditions and entering the supercritical domain. The term fluid is used because, under these conditions, there is no longer a clear distinction between a liquid and a gas phase. The non-conventional behavior of thermophysical properties makes the modeling of supercritical fluid flows a most challenging task. In the present work, a RANS computational method following an incompressible but variable density approach is devised on which the performance of several turbulence models is compared in conjunction with a high accuracy multi-parameter equation of state. Also, a suitable methodology to describe transport properties accounting for dense fluid corrections is applied. The results are validated against experimental data, becoming clear that there is no trend between turbulence model complexity and the quality of the produced results. For several instances, on...
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Natural flight has consistently been the wellspring of many creative minds, yet recreating the propulsive systems of natural flyers is quite hard and challenging. Regarding propulsive systems design, biomimetics offers a wide variety of... more
Natural flight has consistently been the wellspring of many creative minds, yet recreating the propulsive systems of natural flyers is quite hard and challenging. Regarding propulsive systems design, biomimetics offers a wide variety of solutions that can be applied at low Reynolds numbers, achieving high performance and maneuverability systems. The main goal of the current work is to computationally investigate the thrust-power intricacies while operating at different Reynolds numbers, reduced frequencies, nondimensional amplitudes, and mean angles of attack of the oscillatory motion of a NACA0012 airfoil. Simulations are performed utilizing a RANS (Reynolds Averaged Navier-Stokes) approach for a Reynolds number between 8.5×103 and 3.4×104, reduced frequencies within 1 and 5, and Strouhal numbers from 0.1 to 0.4. The influence of the mean angle-of-attack is also studied in the range of 0∘ to 10∘. The outcomes show ideal operational conditions for the diverse Reynolds numbers, and results regarding thrust-power correlations and the influence of the mean angle-of-attack on the aerodynamic coefficients and the propulsive efficiency are widely explored.
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The present work is dedicated to the study of cryogenic nitrogen jets under supercritical chamber conditions with the objective of simulating the process of fuel injection inside a combustion engine. In order to do so, a numerical... more
The present work is dedicated to the study of cryogenic nitrogen jets under supercritical chamber conditions with the objective of simulating the process of fuel injection inside a combustion engine. In order to do so, a numerical simulation using a RANS model was performed over two case studies previously analyzed by other authors both in experimental and numerical studies. The result obtained by the present numerical approach were then compared with previous results and this way accessed the capabilities of RANS approach using a k-e turbulence model in which the density is calculated through the mixture fraction value to correctly model cryogenic jets at supercritical conditions. The results show the ability to achieve good agreement with other studies for the axial density distribution however for other parameters like the jet spreading angle the same agreement was not found.
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The present paper describes a tool developed in-house for the modeling of free-falling water droplet cooling processes. A two-way coupling model is employed to account for the interactions between the droplets and the carrier fluid,... more
The present paper describes a tool developed in-house for the modeling of free-falling water droplet cooling processes. A two-way coupling model is employed to account for the interactions between the droplets and the carrier fluid, following a Eulerian–Lagrangian approach. In addition, a stochastic separated flow technique is employed, involving random sampling of the fluctuating fluid velocity. In physical modeling, two empirical correlations are considered for determining the heat and mass transfer coefficients, with the possibility of accounting for vibrations. The numerical results indicate the preponderance of the interactions between droplet and carrier fluid at various humidity ratios.
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In Liquid Rocket Engines, higher combustion efficiencies come at the cost of the propellants exceeding their critical point conditions and entering the supercritical domain. The term fluid is used because, under these conditions, there is... more
In Liquid Rocket Engines, higher combustion efficiencies come at the cost of the propellants exceeding their critical point conditions and entering the supercritical domain. The term fluid is used because, under these conditions, there is no longer a clear distinction between a liquid and a gas phase. The non-conventional behavior of thermophysical properties makes the modeling of supercritical fluid flows a most challenging task. In the present work, a Reynolds Averaged Navier Stokes (RANS) computational method following an incompressible but variable density approach is devised on which the performance of several turbulence models is compared in conjunction with a high accuracy multi-parameter equation of state. In addition, a suitable methodology to describe transport properties accounting for dense fluid corrections is applied. The results are validated against experimental data, making it clear that there is no trend between turbulence model complexity and the quality of the pr...
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ABSTRACT Laser Doppler measurements provide information on the flowfield created by twin impinging jets aligned with a low velocity crossflow. The experiments were carried out for a Reynolds number based on the jet exit conditions of Re... more
ABSTRACT Laser Doppler measurements provide information on the flowfield created by twin impinging jets aligned with a low velocity crossflow. The experiments were carried out for a Reynolds number based on the jet exit conditions of Re j=4.3×10^4, an impingement height of 20.1 jet diameters and for a velocity ratio between the jet exit and the crossflow V R=V j/U o of 22.5, and an interjet spacing of S=6D. The results show a large penetration of the first (upstream) jet that is deflected by the crossflow and impinges on the ground, giving rise to a ground vortex due to the collision of the radial wall and the crossflow that wraps around the impinging point like a scarf. The second jet (located downstream) it is not so affected by the crossflow in terms of deflection, but due to the downstream wall jet that flows radially from the impinging point of the first jet it does not reach the ground. The results indicate a new flow pattern not yet reported so far, that for a VSTOL aircraft operating in ground vicinity with front wind or small forward movement may result in enhanced under pressures in the aft part of the aircraft causing a suction down force and a change of the pitching moment towards the ground. © 2012 by the American Institute of Aeronautics and Astronautics, Inc.
Laser-Doppler measurements of the velocity characteristics of the flowfield resulting from the impingement of two and three jets against a wall through a low-velocity crossflow are presented and discussed together with visualization of... more
Laser-Doppler measurements of the velocity characteristics of the flowfield resulting from the impingement of two and three jets against a wall through a low-velocity crossflow are presented and discussed together with visualization of the flow. The experiments have been carried out for a velocity ratio between the jets and the crossflow of 30, for a Reynolds number based on the jet exit of 105,000, and for the jet exit five jet-diameters above the ground plate. This study provides a basis for understanding the physical mechanisms acting in impingement-cooling type of flows and in the flowfield created underneath a vertical short take-off aircraft, as well as reliable data to evaluate the numerical solutions of the equations of motion which use turbulence models in order to predict this type of flows. The results include mean and turbulent velocities and quantify the large effects of flow distortion on the turbulent structure of complex three-dimensional impingement and fountain flows.
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ABSTRACT 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 presented and discussed together with flow visualization. In the present... more
ABSTRACT 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 presented and discussed together with flow visualization. In the present study velocity ratios between the boundary layer and the wall jet of 0.5 and 0.62 were considered. Two secondary vortices were found upstream the separation point for the highest velocity ratio. The angle of deflection of the upwash flow was found to decrease with the velocity ratio, while the wall jet penetration increases.