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- The Influence of Front Wing Pressure Distribution on Wheel Wake Aerodynamics of a F1 CarPublication . Martins, Daniel; Correia, João; Silva, AndréThe present study focuses on investigating the aerodynamic interaction between a three-element wing and wheel in ground effect, following the Formula One regulation change set for 2022, among which is the simplification of the front wing. This was accomplished by conducting a three-dimensional computational fluid dynamics analysis, using a Detached-Eddy Simulation approach, on a simplified one-quarter model of a Formula One racing car. The main goal was to examine how changing the front wing pressure distribution, by changing the incidence of the second flap, affected the wheel wake. The flow investigation indicated that the wheel wake is influenced by the flap configuration, which is mainly due to the fact that different flap configurations produce different upwash flow fields, leading to a variation of the separation point on top of the tire. As the separation point moves rearwards, the downwash generated in the central region (for a vertical plane) of the wheel wake increases incrementally, leading to a resultant wake that is shorter and further apart. The force investigation showed that the proximity between the region of instability (i.e., vortex breakdown) and the wing’s trailing edge influences the behavior of the transient oscillations, regarding the forces acting on the wing: detecting higher drag force fluctuations, when compared to downforce fluctuations.
- Predicting the NACA0012-IK30 Airfoil Propulsive Capabilities with a Panel MethodPublication . Camacho, E. A. R.; Marques, Flávio D.; Silva, A. R. R.Unsteady airfoils play a pivotal role in comprehending diverse aerospace applications, being one of those flapping propulsions. The present paper studies this topic by bringing back an old unsteady panel method to juxtapose its results against CFD data previously obtained. The central objective is to revive the interest in these reduced order models in the topic of unsteady airfoils, which can be extended to model highly nonlinear effects while keeping computational resources fairly low. The findings reveal that while the potential flow-based UPM (Unsteady Panel Method) struggles to accurately capture the airfoil’s propulsive power, it remains adept at estimating consumed power. Moreover, an investigation into the pressure coefficient shows the potential benefits of UPM in contexts where flow separation can be disregarded. Despite inherent limitations, these simplified methodologies offer an effective preliminary estimation of flapping airfoil propulsive capabilities.
- 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.
- Multiple impinging jet air-assisted atomizationPublication . Pizziol, Bruno; Costa, Mário; Panão, Miguel; Silva, A. R. R.The growth of the aviation sector triggered the search for alternative fuels and continued improvements in the combustion process. This study addresses the technological challenges associated with spray systems and the concern of mixing biofuels with fossil fuels to produce alternative and more ecological fuels for aviation. This work proposes a new injector design based on sprays produced from the simultaneous impact of multiple jets, using an additional jet of air to assist the atomization process. The results evidence the ability to control the average droplet size through the air mass flow rate. Depending on the air mass flow rate there is a transition between atomization by a hydrodynamic breakup of the liquid sheet formed on the impact point, to an aerodynamic breakup mechanism, as found in the atomization of inclined jets under cross-flow conditions. The aerodynamic shear breakup deteriorates the atomization performance, but within the same order of magnitude of the atomization efficiency. Finally, despite using different configurations (2, 3 and 4-impinging jets), the outcome is similar is terms of the sizes of drops produced, although increasing the number of impinging jets also implies some deterioration of the atomization efficiency.
- Dynamics of a gyrostat satellite with the vector of gyrostatic moment tangent to the orbital planePublication . Morais, Renato; Santos, Luis; Silva, André; Melício, RuiIn this paper, a gyrostat satellite in a circular orbit with its gyrostatic moment tangent to the orbital plane and collinear with the orbital speed is studied regarding its equilibria, bifurcation of equilibria, and asymptotic stability conditions. In the general case, where any gyrostat angular momentum is aligned with any of the orbital coordinate frames, interesting results arose regarding its equilibria bifurcation regarding conditions near to the ones presented in this paper, namely equilibria regions outside their main regions near to the orbital plane tangent. For equilibria and bifurcation of equilibria, a symbolic-numerical method is used to obtain the polynomial equations in function of non-dimensional parameters whose roots are equivalent to the number of equilibria positions. For the asymptotic stability, the results are tested using the Lyapunov stability theory scheme.