Associate Laboratory of Energy, Transports and Aeronautics

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Publications

Temperature Field Validation on Supercritical Coaxial Injection

Publication . Magalhães, Leandro; Silva, A. R. R.; Barata, Jorge M M

In 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.

2022-06-27Conference object

Open access

Influence of Trailing-Edge Shape on the Propulsive Performance of a Plunging Flat Plate

Publication . Gonçalves, Sullivan Benjamim Seixas; Camacho, Emanuel; Silva, A. R. R.

Unsteady aerodynamics is the study of flows that pass an object subjected to oscillations, which has a strong association with bioinspired flows and rotor dynamics. The central objective of the paper is to study the propulsive characteristics of two plates at a Reynolds number of 3.1x10^3 with straight and sharp trailing edges. The reduced frequency is kept between 1.0 and 5.0 with a nondimensional amplitude ranging between 0.125 and 0.500. The problem was solved numerically using CFD (Computational Fluid Dynamics), and results show that differently from what is usually observed in airfoils, the mean thrust coefficient does not increase monotonously with the reduced frequency, having a dip around k = 3.0. The same is not verified for the mean power coefficient, which increases continuously with the reduced frequency. Two phenomenon responsible for the reduction of the mean thrust coefficient is identified. Through analysis of pressure contours around the flat plates, a low-pressure zone was seen near the trailing edge, creating a suction effect in that zone. The influence of k on the formation of the LEV is analyzed, via its approximate radius, evidencing a behavior similar to the mean Ct . Furthermore, the trailing-edge shape revealed to be an important factor on thrust reduction.

2022-06-20Conference object

Embargoed access

Parametric Study of a Plunging NACA0012 Airfoil

Publication . Camacho, E. A. R.; Neves, Fernando M. S. P.; Silva, André; Barata, Jorge M M

Natural flight has always been the source of imagination for the Human being, but reproducing the propulsive systems used by animals is indeed complex. New challenges in today’s society have made biomimetics gain a lot of momentum because of the high performance and versatility these systems possess when subjected to the low Reynolds numbers effects. The main objective of the present work is the computational study of the influence of the Reynolds number, frequency and amplitude of the oscillatory movement of a NACA0012 airfoil in the aerodynamic performance for a constant angle of attack over time. The thrust and power coefficients are obtained which together are used to calculate the propulsive efficiency. The simulations were performed using ANSYS Fluent with a RANS approach for Reynolds numbers between 8,500 and 34,000, reduced frequencies between 1 and 5, and Strouhal numbers from 0.1 to 0.4. The aerodynamic parameters were widely explored as well as their interaction, obtaining optimal operational condition zones for the different Reynolds numbers studied.

2020-06-02Journal article

Open access

Asteroid Impacts on the Ocean and Its Short-term Consequences: a Portuguese Case Study

Publication . Morais, Renato; Santos, Luís; Silva, A. R. R.; Melício, Rui

Any location on Earth might be considered a subject to an asteroid impact because, as previous studies show, they are a proven global threat. the consequences of a collision could be catastrophic, even though such events are rare to occur in a person’s lifetime. Tsunami waves can constitute the greatest threat as the Earth’s surface is mostly water, making the probability of a water impact greater than a ground impact. This work expands the knowledge about asteroid impacts on the ocean and their short-term regional consequences. Three asteroids were assumed to impact the Earth: (1) the 2015 JJ asteroid with a 130 m diameter, (2) the 2020 FA5 asteroid with a 210 m diameter, and (3) the Apophis asteroid, a 370 m wide asteroid. We evaluated the consequences of all impacts, at a 45 degree angle, for a specific case study, where the chosen impact location was the midpoint between Portugal’s mainland, Azores, and Madeira Islands. The cratering process, overpressure, induced thermal radiation, and tsunami waves were assessed, along with the global effects. The overpressure mainly causes structural damage. The thermal radiation has too short a range to reach the studied localities. The tsunami is undoubtedly the most far-reaching and threatening effect of an asteroid impact in the ocean.

2022-06-19Conference object

Open access

The Addition of Particles to an Alternative Jet Fuel

Publication . Ferrão, Inês; Mendes, Miguel; Moita, A. S.; Silva, André

The expansion of the research on nanoscale particles demonstrates several advantages in terms of stability and an increased surface area to volume ratio compared to micron-sized particles. Based on this, the present work explores the addition of aluminum particles in hydrotreated vegetable oil (HVO), an alternative jet fuel. To evaluate the influence of particle sizes, nano and micron particles (40 nm and 5 μm) in a particle concentration of 0.5 wt.% were stably suspended in HVO. This study evaluates droplet combustion with an initial diameter of 250 μm in a drop tube furnace under different furnace temperatures (600, 800, 1000 °C). A high magnification lens coupled with a high-speed camera provides qualitative and quantitative data regarding droplet size evolution and micro-explosions. Pure HVO and Jet A-1 were also tested for comparison purposes. The results reveal that the addition of aluminum particles enhances the alternative jet fuel combustion. Furthermore, decreasing the particle size and increasing the furnace temperature enhances the burning rate compared to the pure HVO. Pure HVO presents a burning rate nearly to 1.75 mm2/s until t/D20 = 0.35 s/mm2 at T = 1000 °C. When nanoparticles are added to HVO in a particle concentration of 0.5 wt.%, an improvement of 24% in burning rate is noticed. Conventional jet fuel and pure HVO do not present any disruptive burning phenomena. However, when aluminum particles were added to HVO, micro-explosions were detected at the end of droplet lifetime, regardless of the particle size.

2022-03-22Journal article

Open access