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- How different are conventional and biofuel sprays applied to aviation? An infodynamic comparative analysisPublication . Ferrão, Inês Alexandra dos Santos ; Panão, Miguel Rosa Oliveira; Mendes, Miguel; Moita, Ana Sofia Oliveira Henriques; Silva, André Resende Rodrigues daThe transition from fossil to sustainable and alternative fuels is imperative to address environmental concerns and meet energy requirements. Thus, the implementation of alternative fuels requires a deeper investigation of spray behavior. This study explores conventional jet fuel (Jet A-1) and hydrotreated vegetable oil (HVO) in terms of breakup length and spray dynamics over a wide range of operating conditions. The normalized mean breakup length was measured, and an empirical correlation was developed based on the experimental data. Focusing on the droplet sizes in fuel sprays, which are critical for optimizing combustion, an informational perspective for comparative analysis was explored. The terms informature, infotropy, and infosensor were introduced to quantify and capture the non-deterministic nature of physical systems. The results revealed similar drop size distributions for HVO and Jet A-1, with the Gamma function effectively characterizing the distributions. Both fuels exhibit spray evolution toward higher complexity states, emphasizing the role of aerodynamic forces and minimum development distance in atomization. The new lexicon of infodynamics views sprays as networks of information flow, with infotropy indicating that both fuels produce sprays with similar degrees of transformation. HVO is endorsed as a viable alternative with broader implications for sustainable aviation solutions and understanding complex engineering processes.
- Predicting airfoil dynamic stall loads using neural networksPublication . Camacho, Emanuel António Rodrigues ; Silva, André Resende Rodrigues da ; Marques, Flávio D.Dynamic stall is an aerodynamic regime characterized by loss of airfoil lift, drag increment, and abrupt changes in the pitching moment. Such effects can couple with structural dynamics where perturbations can be easily amplified, making this a critical phenomenon that jeopardizes operational safety. Hence, there is always the need to constantly study the basics of dynamic stall and provide newer predictive models that can take advantage of the current interest peak in artificial intelligence. The present work builds upon that need, exploring the ability of a simple feed-forward network to predict the oscillation cycle of a pitching airfoil experiencing from light to deep stall of a NACA0012 airfoil close to a Reynolds number of approximately 1.1x10^6. The proposed neural network uses the angle of attack and its rate of change as inputs, then estimates the whole aerodynamic cycle at once, outputting an aggregated vector of drag, lift, and pitching moment coefficients. The training phase was conducted using a database containing several conditions obtained from experimental tests, with a strict convergence criterion of R^2=0.99 for both training and test datasets. Results show that the neural network, even in the least-performing conditions, can capture the aerodynamics and overall tendencies, even if some dynamics are underrepresented in the training dataset. The present work brings down the complexity of methodology while demonstrating that a simplistic architecture can still offer an accurate dynamic stall model.
- Splashing correlation for single droplets impacting liquid films under non-isothermal conditionsPublication . Rodrigues, Daniel de Almeida Vasconcelos ; Barata, Jorge Manuel Martins ; Silva, André Resende Rodrigues daThe droplet impact phenomenon onto liquid films is predominant in a variety of modern industrial applications, including internal combustion engines and cooling of electronic devices. These are characterised by heat and mass transfer processes, such as evaporation, condensation and boiling. However, studies regarding droplets and liquid films under non-isothermal conditions are scarce in the literature and do not explore temperature-dependent phenomena. Due to this, the main objective of this work is to evaluate the influence of temperature on the splashing occurrence of single droplets impinging onto liquid films under the presence of a heat flux. The crown evolution is evaluated qualitatively to provide insight regarding breakup mechanisms. Water, n-heptane and n-decane are the fluids considered for the current study, as these provide a wide range of thermophysical properties and saturation temperatures. The splashing dynamics are evaluated by varying the droplet impact velocity and dimensionless temperature of the liquid film. Qualitative results show that an increase in the liquid film temperature leads to the transition from spreading to splashing, which is less evident for fuels in comparison with water. For water and n-heptane, the formation of cusps on the crown rim is promoted, which is associated with ligament breakup. For n-decane, the crown rims are relatively homogeneous in terms of shape and size, whereas the atomisation process varies a function of the liquid film temperature. Visually, the secondary droplets exhibit a greater size in comparison with lower temperatures. Transitional regimes display some irregularities, such as splashing suppression/reduction, which require further attention. In terms of splashing correlation, the authors propose to develop a non-splash/splash boundary for both iso- and non-isothermal conditions. Results show that the splashing threshold is dependent on the thermophysical properties and the dimensionless temperature of the liquid film.
- Thrust force assessment of a MFC-actuated tail-like robotic fish using Unsteady Panel MethodPublication . Silva, Maíra Martins da ; Camacho, Emanuel António Rodrigues ; Silva, André Resende Rodrigues da ; Marques, Flávio D.Fish-like robots are used in various fields, such as environmental monitoring and underwater exploration. These devices are designed to emulate the motion of a real fish. They can have flexible bodies to mimic body/caudal-based locomotion patterns or fins to mimic median/paired fin-based locomotion patterns. Standard propulsion methods include oscillating fins, flapping tails, and body undulations. This work investigates a robotic fish with a flexible tail actuated by a Macro-Fiber Composite (MFC) pair in a bi-morph configuration. This device is designed to mimic body/caudal-based locomotion patterns; therefore, it should present propulsion capabilities due to its body undulations. These propulsion capabilities are assessed using the Unsteady Panel Method for different sinusoidal inputs. This method requires the device’s kinematics, which is derived using an analytical model based on the Euler–Bernoulli beam theory, considering the electro-mechanical coupling of the actuators. The mean thrust force derived using the Unsteady Panel Method is compared with the actual mean thrust acquired during an experimental campaign. The experimental and numerical results indicated that higher thrust forces can be achieved when the device is excited in its second resonance frequency. These results are in line with Lighthill’s findings.
- Flapping Airfoil Aerodynamics using Recurrent Neural NetworkPublication . Pereira, João A.; Camacho, Emanuel A. R.; Marques, Flávio D.; Silva, AndréThe recent increase in interest in artificial intelligence and neural networks has stirred up various industries. Inevitably, its application will trickle down to the most fundamental studies, for instance, unsteady aerodynamics. The present paper serves the purpose of exploring the ability of a recurrent neural network to predict flapping airfoil aerodynamics, in particular the lift coefficient of a plunging NACA0012 airfoil. Thus, a neural network is designed and trained using motion parameters, such as motion frequency and effective angle of attack, to output the instantaneous lift coefficient over a plunging period. Training data is generated using a panel code (HSPM) for fast generation and early testing. Results show that the neural network can adequately predict the lift coefficient for various conditions, including plunging kinematics that are far from the training domain. Future work will build on this framework and extend it to other aerodynamic coefficients using CFD results and experiments, which should enhance the value of the estimates.
- Dynamic Stall Mitigation Using a Deflectable Leading Edge: The IK30 MechanismPublication . Camacho, Emanuel A. R.; Silva, A. R. R.; Marques, Flávio D.One major problem affecting rotor blade aerodynamics is dynamic stall, characterized by a series of events where transient vortex shedding negatively affects drag and lift, leading to abrupt changes in the wing’s pitching moment. The present work focuses on the mitigation of such effects by using a modified NACA0012 airfoil—the NACA0012-IK30 airfoil—previously used for thrust enhancement in flapping propulsion. An experimental rig is designed to study the advantages of a deflectable leading edge on a plunging and pitching wing, more specifically its influence on the aerodynamic coefficients over time. In the first stage, results indicate that the proposed IK30 mechanism does mitigate the stall effects under static conditions, with stall visualization data corroborating it. Regarding time-varying conditions, the data presents the adequacy of the proposed geometry under different plunging and pitching conditions, which, when correctly used, can mitigate or even eradicate the adverse effects of dynamic stall experienced, leading to significant drag reductions and modest lift enhancements. In the absence of a dynamic stall, the movable leading edge can also provide operational advantages, where it does not negatively affect drag or lift but can reduce the pitching moment intensity by indirectly shifting the pressure center. This study contributes to the long-standing discussion on how to mitigate the adverse effects of dynamic stall by providing an innovative yet simple solution.
- Influence of aluminum nanoparticles in alternative fuel: Single droplet combustion experiments and modelingPublication . Ferrão, Inês; Mendes, Tomás; Mendes, Miguel; Moita, A. S.; Silva, A. R. R.In this work, the effect of adding aluminum nanoparticles on hydrotreated vegetable oil was investigated experimentally and numerically in terms of nanofuel stability and single droplet combustion. The purpose is to understand the phenomena related to isolated droplet combustion when metallic particles are added to a liquid biofuel. Falling droplet combustion experiments were conducted in a drop tube furnace at two different furnace temperatures (800 C and 1000 C) using a high-speed camera coupled with a high magnification lens to investigate the droplet size evolution as disruptive burning phenomena. In numerical terms, a simplified macroscopic model was developed to predict the burning behavior of isolated nanofuel droplets, considering hexadecane as a surrogate fuel for the biofuel. The results reveal that adding nanoparticles resulted in a departure from the -law. Moreover, an increase in the overall droplet burning rate was observed, and according to the numerical results, nanoparticle radiation absorption is the responsible mechanism. Micro-explosions occurred for all nanofuels, and this disruptive burning behavior substantially influenced the droplet lifetime.
- Housekeeping System for Suborbital Vehicles: VIRIATO Mock-Up Vehicle Integration and TestingPublication . Rodrigues, Geraldo; Arribas, Beltran; Melício, Rui; Gordo, Paulo; Valério, Duarte; Casaleiro, J.; Silva, AndréThe work presented in this paper regards the improvement of a housekeeping system for data acquisition of a suborbital vehicle (VIRIATO rocket or launcher). The specifications regarding the vehicle are presented and hardware is chosen accordingly, considering commercial off-the-shelf components. Mechanical and thermal simulations are performed regarding the designed system and a physical prototype is manufactured, assembled and programmed. Functional and field test results resorting to unmanned aerial vehicles, as well as the system’s integration within VIRIATO project’s mock-up vehicle, are presented. These tests demonstrate the viability of this system as an independent data acquisition system, and simulation results show that commercial off-the-shelf components have the capability of surviving expected launch environments.
- 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.
- List of Arrivals 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 arrivals 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, 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.