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Browsing by Author "Carvalho, Pedro dos Santos Duarte"

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  • Laser Doppler Measurements of Twin Impinging Jets Aligned with a Crossflow
    Publication . Barata, Jorge M M; Carvalho, Pedro dos Santos Duarte; Neves, Fernando M. S. P.; Silva, André; Vieira, Diana; Durão, Diamantino
    This paper presents a detailed analysis of the complex flow beneath two impinging jets aligned with a low-velocity crossflow which is relevant for the future F-35 VSTOL configuration, and provides a quantitative picture of the main features of interest for impingement type of flows. The experiments were carried out for a Reynolds number based on the jet exit conditions of Rej = 4.3  104, an impingement height of 20.1 jet diameters and for a velocity ratio between the jet exit and the crossflow VR = Vj/Uo of 22.5. The rear jet is located at S = 6 D downstream of the first jet. 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 rear 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.
    2014-07Journal article Open access Show more
  • Numerical and Experimental Study of Two Impinging Jets in a Row through a Crossflow
    Publication . Vieira, Diana; Silva, André; Neves, Fernando M. S. P.; Carvalho, Pedro dos Santos Duarte; Barata, Jorge M M
    An experimental and numerical study is carried out to investigate the flowfield created by twin impinging jets aligned with a low velocity crossflow. The mean velocity, velocity fluctuation and visualization in the impingement region were obtained for a Reynolds number based on the jet exit conditions of Rej=4.3x104, an impingement height of 20.1 diameter and for a velocity ratios between the jet exit and the crossflow VR=Vj/Uo of 22.5, 33.7 and 43.8 with interject spacing, S of 6D. The experimental results show a large penetration of the first (upstream) impinging jet, giving rise to a ground vortex due to the collision of the radial wall jet 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 it does not reach the ground due to the downstream wall jet that flows radially from the impinging point of the first jet along the ground. The results indicate a new flow pattern not yet reported so far, in which a VSTOL aircraft operating in ground vicinity with front wind or small forward movement may result in enhanced negative pressures in the underside of the aircraft causing a pitching moment and a suction down force towards the ground. To extend the experimental results, the flow was also numerically simulated using a Reynolds Averaged Navier-Stokes formulation with the "k-ε" turbulence model.
    2013-01-05Journal article Embargoed access Show more
  • Numerical study of aerodynamically flow interaction
    Publication . Carvalho, Pedro dos Santos Duarte; Silva, André Resende Rodrigues da
    Esta dissertação é constituída por dois estudos que focam a interacção entre jactos múltiplos em diferentes configurações de escoamento distribuídos em dois temas, o primeiro tema denominado ‘Numerical Study of Aerodynamically Enhanced Mixing’ e o segundo ‘Numerical Study of Twin Impinging Jets Aligned with Low Velocity Crossflow’. O primeiro tema abordada a mistura turbulenta de jactos coaxiais em duas configurações, escoamento confinado e não confinado, para razões de diâmetro inferior a 2 sendo diversas as áreas de aplicação como ejectores, bombas de jactos, câmaras de combustão para motores a jacto e particularmente, motores turbofan com baixa razão de bypass. Simulou-se computacionalmente camadas de corte bidimensionais em escoamentos de mistura de jactos utilizando o modelo de turbulência k – ε, sendo comparados os dados numéricos resultantes da simulação com dados experimentais revelando boa capacidade de simulação para este tipo de escoamento por parte do modelo adoptado. Contudo de salientar a ausência total de qualquer tipo de recirculação apesar da forte interacção verificada entre jactos, e a região de interacção entre o jacto exterior e o jacto interior apresentou elevados níveis de energia cinética turbulenta, na configuração com superfície superior sólida. Múltiplos jactos incidentes alinhados com escoamento cruzado de baixa velocidade representa o segundo tema abordado nesta dissertação sendo um tema de interesse para as mais diversas áreas, entre as quais, o arrefecimento de equipamentos, dispersão de poluentes e em especial para aeronaves VSTOL, ou seja aeronaves com capacidade de descolagem e aterragem vertical ou em curtas distâncias focando particularmente a aeronave F-35 aquando operando em modo VSTOL próximo do solo. Neste estudo simulou-se computacionalmente jactos múltiplos tridimensionais alinhados com escoamento cruzado embatendo numa superfície sólida para 3 razões de velocidade, comparando-se dados numéricos resultantes da simulação computacional com dados experimentais concluindo-se que o modelo computacional subdimensiona o escoamento apesar de terem sido encontrados ground vortex para as duas razões de velocidade mais elevadas.
    2012-10Master thesis Open access Show more