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- Numerical Study of Freezing DropletsPublication . Magalhães, Leandro Barbosa; Silva, André Resende Rodrigues daThe present work is devoted to the numerical study of freezing processes which have become of major importance in aeronautical engineering. The most common causes of structural damage to aircrafts result from climacteric changes such as lightning strikes and icing of the wing’s leading edges or empennage, which turns the smooth airflow over the wings into turbulent. At subzero temperatures, icing spreads from the leading to the trailing edge, affecting a greater percentage of the wings. As a result there is a need to study and adapt existing physical and mathematical models to achieve a better approximation to real life situations in order to mitigate the occurrence of incidents and accidents involving aircraft for a better continuous airworthiness. The theoretical predictions are compared against experimental data and the numerical analysis is conducted to provide insight into heat and mass transfer processes under several humidity conditions.
- 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.
- Description of an incompressible variable density approach for the description of supercritical fluids flowsPublication . Magalhães, Leandro; Cleto, João M. N.; Silva, A. R. R.; Barata, Jorge M MThe simplification of the incompressible but variable density jet is based on the visualization of data similarity. Given the initial encouraging results obtained in the past, we extend, in the present paper, this hypothesis to a broader range of conditions to ascertain its applicability and its role as an alternative to the more commonly fully-compressible formulations encountered in the literature. Transcritical and supercritical injection conditions are considered for nitrogen, which works as a surrogate for the oxygen-hydrogen mixture combination, characteristic of liquid rocket propulsion. A close agreement is found between experiments and numerical results in terms of axial profiles and jet spreading rates.
- List of Departures from LIS Airport from March 7, 2023 until March 13, 2023Publication . Fernandes, Ricardo; Magalhães, Leandro; Ferreira, Ana FilipaThis document contains statistical data from one week, including the real number of departures for each type of aircraft (engine) at Lisbon airport (LIS). The analysis was conducted from March 7, 2023 until March 13, 2023. The chosen period was based on the application of the randomness criterion and availability to obtain this information. The traffic sample for the referred period is obtained from an online database (Flight Radar 2024) which keeps data relatively to all the arrivals and departure from LIS airport. The data acquired by the database is from different sources, the main one being Automatic Dependent Surveillance-Broadcast (ADS-B). According to the analyzed data available at ANAC, the period under analysis, regarding the monthly traffic variation at the airport, represents approximately an average month (only around 4.6% below the average monthly movements for the year 2023), which seems appropriate for this analysis given that the aim is to achieve an annual average of movements and emissions. This fact has been observed for the current year, a fact that is in line with previous years. It was also observed that February corresponds to the month with the lowest air traffic, and the month of August represents the peak of operations at the airport under analysis.
- Computational Modeling of Water Droplets Under Cooling and Freezing ConditionsPublication . Meireles, Rúben D. S. O.; Magalhães, Leandro; Silva, A. R. R.; Barata, Jorge M MThe crystallization of water droplets is a ubiquitous phenomenon, which plays afundamental role in many natural and artificial processes. This phenomenon gainedparticular interest in the aeronautical industry due to ice accretion on lifting surfaces andengine intakes. A performance study is made of several models for predicting cooling and freezing phenomena, ranging from one- and two-way coupling to full-fledged four-stage freezing methodologies. First, a performance study is made of the one- and two-way coupling methodologies in the portrayal of the interaction of the particles and the surrounding gas on free-falling water droplets with diameters ranging from 3 to 6 mm and relative humidity ratios of 0.29, 0.36. 0.52 and 1.00. Then a generalized four-stage freezing model is implemented, where the temperature evolution of a suspended water droplet is tracked, adding to the cooling in the free-falling conditions, the recalescence and solidification stages. The results indicate that, for high relative humidity ratio, the interaction particles-medium is preponderant and needs to be accounted for, which does not take place for low relative humidity ratios, where one-way coupling seems to be suitable approximation. Lastly, the full stage freezing model was able to capture the experimental trend of recalescence and solidification stages.
- Turbulence Modeling Insights into Supercritical Nitrogen Mixing LayersPublication . Magalhães, Leandro; Carvalho, Francisco; Silva, A. R. R.; Barata, Jorge M MIn 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 produced results. For several instances, one- and two-equation turbulence models produce similar results. Finally, considerations about the applicability of the tested turbulence models in supercritical simulations are given based on the results and the structural nature of each model.
- Heat transfer effect on the modeling of jets under supercritical and transcritical conditionsPublication . Magalhães, Leandro; Silva, A. R. R.; Barata, Jorge M MThe injection of nitrogen under supercritical and transcritical conditions, where the injection temperature is below nitrogen’s critical point, but the pressure is above it, is considered in this paper. While the scientific community recognizes that the sharp gradients of the different thermophysical parameters make it inappropriate to employ a two-phase flow modeling at conditions above the critical point, the issue is not restrained to the mere representation of turbulence for a mono-phase flow. Instead, a quantitative similarity with gas-jet-like behavior led to proposing an incompressible but variable density hypothesis suitable for describing supercritical and sub/near-critical conditions. Presently, such an approach is extended and assessed for a configuration including injector heat transfer. As such, axial density and temperature decay rates and jet spreading rates of density and temperature are evaluated, indicating a higher mixing efficiency in the supercritical regime and an overall dominance of heat propagation over momentum transport, with a greater preponderance in the supercritical regime.
- Temperature Field Validation on Supercritical Coaxial InjectionPublication . Magalhães, Leandro; Silva, A. R. R.; Barata, Jorge M MIn the present manuscript, we report on the numerical simulation of coaxial nitrogen injection under subcritical and supercritical conditions, where the inner stream is recessed concerning the coaxial one. An incompressible but variable density description of supercritical phenomena is pursued as an alternative to more established compressible formulations, in which we extend past analysis focusing on the evaluation of density to the temperature field validation, according to the available experimental data. The results indicate that recirculation regions are formed as expected at either the inner jet axis or at the post tip between both streams. Furthermore, it is found that the transition threshold between the blockage effect depends on the momentum ratio and differs between subcritical and supercritical conditions.
- Locally variable turbulent Prandtl number considerations on the modeling of Liquid Rocket Engines operating above the critical pointPublication . Magalhães, Leandro; Silva, A. R. R.; Barata, Jorge M MThe general idea behind the present work is to study the injection of a cryogenic liquid numerically into rocket engines, where propellant conditions are above the thermodynamic critical point, for a non-reactive case. The singular behavior of thermodynamic and transport properties at and around the critical point makes this a most challenging task. While mass diffusivity, surface tension, and latent heat are zero at the critical point, isentropic compressibility, specific heat, and thermal conductivity tend to infinity. As a result, the distinction between liquid and solid phases disappears. Ultimately, the fluid has liquid-like density and gas-like properties, mass diffusion replaces vaporization as a governing parameter, and it dominates over jet atomization. Henceforth, any model used incorporates as close as possible to reality, the variation of thermodynamic and transport properties. An incompressible variable-density flow is simulated using Favre averages (FANS) with a locally variable turbulent Prandtl number, taking into account the potential core, transition, and the self-similar region of the jet. The use of a turbulence model with a variable turbulent Prandtl number arises from the ineffectiveness in predicting observed anisotropies in the thermal eddy diffusivity fields when this value is taken as a constant. Favre averaged conservation equations for mass, momentum, and energy are coupled with the k- two-equation turbulence model and discretized following the third order upwind QUICK scheme. Stability and accuracy of the results are maintained through a careful selection of the parameters involved in the models. The use of the conservation equation for energy is justified as an indirect means to evaluate the thermal field. Results are compared with experimental cases for validation purposes as well as LES computations for performance comparison and evaluation of the degree of model complexity needed to achieve satisfactory results.
- Characterization of a Two-way Coupling Approach for the Simulation of Fluid Flows under Cryogenic ConditionsPublication . Meireles, Rúben D. S. O.; Magalhães, Leandro; Silva, A. R. R.; Barata, Jorge M MIce formation at lifting surfaces and engine intakes is a significant issue affecting regular aircraft operation. The icing on a wing’s leading edge perturbs the airflow around the wing, contributing to a decrease in lift and increasing drag. A step towards the understanding of droplet dynamics under cryogenics is made in the present work. An in-house developed tool is used to study the impact of droplet diameter and air humidity ratio in free-falling water droplets’ flow dynamics. The 3D Navier-Stokes equations are solved in a RANS-based two-way coupling model, which considers that the carrier fluid properties are modified by the presence of a dispersed phase, accounting for mass exchange momentum and energy between them. A Lagrangian/Eulerian formulation is employed to model each of the considered phases. The results obtained are compared with a one-way modeling approach and experimental data to infer the interacting phases’ effect in the overall process dynamics. In this way, it is possible to conclude that for high humidity content, this interaction is predominant and, consequently, needs to be taken into consideration. However, for low humidity ratios, the one-way coupling is a sufficient approximation to the experimental data.
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