Estudo do escoamento atmosférico no Centro de Lançamento de Alcântara (CLA) através de medidas de torre anemométrica e em túnel de vento

AUTOR(ES)
DATA DE PUBLICAÇÃO

2007

RESUMO

The atmospheric flow at the Alcantara Launching Center (CLA), which is localized near a 50 m cliff, was studied through (i) the analysis of wind data that were measured during the periods from 1995 to 1999 (base years) and from 2004 to 2005 (for validation), at six levels of a 70 m anemometric tower (TA), which is placed 200 m downwind of the cliff, near a rocket launching pad, and (ii) wind tunnel (TV) experiments, using a 1:1000 geometric scale and floor level configurations to represent the cliff and its downwind roughness. The data at the TA determined that the roughness velocity u* was equal to 0.32 ± 0.13 m/s (0.46 ± 0.11 m/s) during the rainy (dry) period, while the roughness length z0 equalled 0.19 ± 0.32 m (0.06 ± 0.05 m) for the rainy (dry) period, thus showing the seasonality of the wind profiles. The exponent α of the velocity power law varied along the yearly months from 0.19 to 0.27, with R2s between 0.88 and 0.99; α decreased with the altitude zn. For a rainy month, the validation of α with 2004 2005 wind data showed estimated velocities greater than the ones observed at the TA, which was possibly due a weaker atmospheric neutrality; however, for a dry month, these velocities were equivalent, thus implying a neutral atmosphere. Finally, the predominant wind direction was from the Northeast, followed by the ones from the North and the East. The TV experiments, with 90° and 70° steps representing the cliff, both with and without additional downwind roughness, did show: (i) a perfect emulation of the ocean wind profile (α = 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) that the highest Reynolds number possible, based on the height of the cliff, was 6.52 x 104 inside this TV, while it reached 3 x107 at the CLA thus, a more powerfull tunnel is needed to emulate this last situation; (iii) that the values of α nearest to the ones obtained at the CLA resulted from the 90° step experiment without any extra covering over the floor, except the upwind carpet; (iv) that the fixing of cubes downwind of the step resulted roughnesses much greater than the ones observed over the CLA vegetation, so possibly emulating urban or industrial situations; (v) that typical characteristics which occur downwind a step were emulated, such as the dettachment and the posterior reattachment of the flow, plus the formation of circulation bubbles; (vi) that the use of more powerfull TVs would certainly permit the emulation of the atmospheric behavior of the CLA. Finally, with the use of a more powerfull TV, besides the replication of the experiments of the present work, experiments with wind incidences on the step with angles other than 90° should be recommended.

ASSUNTO(S)

rugosidade superficial meteorology túnel de vento penhasco reynolds number número de reynolds anemômetro de fio quente cliff meteorologia hot wire ane atmosfera neutra

ACESSO AO ARTIGO

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