Escoamento atmosférico no Centro de Lançamento de Alcântara (CLA): parte II - ensaios no túnel de vento

Abstract

RESUMOEstudou-se o escoamento atmosférico no Centro de Lançamento de Alcântara (CLA), localizado junto a uma falésia de 50 m de altura, através de simulações em túnel de vento (TV) do CTA/ITA, na escala geométrica 1:1000, com a realização de quatro diferentes ensaios. No TV, os ensaios com degraus de 90° e de 70°, correspondentes à falésia, ambos sem e com simulação de rugosidade adicional a sotavento deles, mostraram: (i) perfeita simulação do perfil de vento oceânico (α = 0,15) sobre a posição do degrau representativo da falésia, utilizando pista de tapete, a montante, para prover a rugosidade necessária; (ii) número de Reynolds máximo possível com comprimento característico igual à altura do degrau neste TV foi 6,52.10 4 , enquanto no CLA é da ordem de 3.10 7 , razão pela qual é necessário um túnel mais potente; (iii) os expoentes mais próximos dos observados em Roballo e Fisch (2008) foram obtidos com um degrau reto, sem nenhum revestimento especial no piso normal do túnel, exceto o tapete a montante do degrau; (iv) a fixação de cubos a jusante do degrau para representar a vegetação resultou em rugosidades bem maiores que as observadas sobre a vegetação do CLA, possivelmente simulando situações urbanas ou industriais; (v) simulação das características típicas do escoamento após o degrau, tais como o descolamento, a formação de bolha de circulação e nova aderência; (vi) uso de TVs mais potentes certamente permitirá a simulação da situação atmosférica do CLA. Palavras chaves: falésia, número de Reynolds, Lei de Potência, perfil de velocidade. ABSTRACT: ATMOSPHERIC FLOW AT THE ALCANTARA LAUCHING CENTER (ALC): PART II-EXPERIMENTS AT A WIND TUNNEL.The atmospheric flow at the Alcantara Launching Center (ALC), which is localized near a 50 m cliff, was studied through analysis of wind tunnel (WT) experiments, using a 1:1000 geometric scale and floor level configurations to represent the cliff and its downwind roughness. The WT experiments, with 90° and 70° steps representing the cliff, both with and without additional downwind roughness, did show: (i) a perfect simulation of the ocean wind profile (a = 0.15) above the position of the step representing the cliff, through the use of a upwind carpeted fetch to provide the necessary roughness; (ii) the highest Reynolds number possible, based on the height of the cliff, was 6.52 x 10 4 inside this WT, while it reached 3 x10 7 at the ACL -thus, a more powerful tunnel is needed to simulate this last situation; (iii) the values of a nearest to the ones obtained at the ACL resulted from the 90° step experiment without any extra covering over the floor, except the upwind carpet; (iv) the fixing of cubes downwind of the step resulted roughness much greater than the ones observed over the ACL vegetation, so possibly simulating urban or industrial situations; (v) typical characteristics which occur downwind a step were simulated, such as the detachment and the posterior reattachment of the flow, plus the formation of circulation bubbles; (vi) the use of more powerful WTs would c...

A Study of the Internal Boundary Layer Generated at the Alcantara Space Center

“…These results were generally lower than those obtained for the ASC for these months, as shown in Fisch [7]. Data of friction velocity u * , aerodynamic roughness length z 0 , the mean velocity profiles and turbulent intensity in the ASC were also studied by Roballo and Fisch [13] and Roballo et al [14]. In the first study, Roballo and Fisch [13] showed that in the rainy months, estimated local velocities are greater than observed ones, perhaps due to weaker atmospheric neutrality, however, in a dry month, they were equivalent, demonstrating the neutral atmospheric conditions.…”

“…In the first study, Roballo and Fisch [13] showed that in the rainy months, estimated local velocities are greater than observed ones, perhaps due to weaker atmospheric neutrality, however, in a dry month, they were equivalent, demonstrating the neutral atmospheric conditions. In the second study Roballo et al [14] used wind tunnel measurements with the hot wire anemometer method. The characteristics of detachment and subsequent reattachment of the flow were observed, as well the recirculation bubbles and the turbulent structure on the top of the coastal cliff.…”

“…In this paper, we define δ IBL as the height when the vertical derivative (z) of the vorticity ω becomes practically zero, which corresponds to an ω profile which is almost constant and an approximately linear variation of velocity with height, as is the case of the Planetary Boundary Layer (PBL) above the IBL. ECLICLA 1 (April 14 -24, 1998, representing the wet season) and ECLICLA 2 (October, [6][7][8][9][10][11][12][13][14][15][16]1998, representing the dry season). ECLICLA is the Portuguese acronym for "Estudos da Camada Limite Interna na região do CLA" which means the study of the IBL at the ASC.…”