An atmospheric Internal Boundary Layer (IBL) occurs when sudden changes in surface roughness disturb wind flows. The region of the Brazilian Alcantara Space Center (ASC), with its rocket launching pad located 150 m downwind of a 40 m coastal cliff, presents the formation of an IBL due to winds blowing inland from the ocean. Numerical simulations using the immersed boundary method, experiments in a wind tunnel using particle image velocimetry, and field observational data obtained from anemometric towers were used to study this IBL. The results demonstrated that it is dependent on the geometry of the coastal cliff: its height is around 17 and 15 m for slopes of the coastal cliff of 90º and 135º, respectively. The numerical results show a good agreement with the experimental data and the field observations, but with an overestimation of the vorticity field. The IBL significantly influences the wind flow at the launching pad.

This research project focuses upon the wake behind a two-dimensional blunt-trailing-edged body. Data are obtained numerically by means of a Direct Numerical Simulation code. The body has an elliptical nose followed by a straight section that ends in a blunt base. The present paper is dedicated to the analysis of the onset of the shedding process. The effort is certainly worthwhile, because, in contrast to the case of the circular cylinder, the boundary layers’s separation points are defined and fixed. This allows a better assessment of the vital influence of the boundary layers upon the wake, in a controlled way. This is not the case for the circular cylinder, because, in this instance, the separation points oscillate in relation to a mean position. In the present analysis, the relationship between the onset of shedding Reynolds number, RehK , and the aspect ratio, AR, is obtained.To this end, a wide range of aspect ratios between 3 and 25, was investigated. The result represented by this relationship is a novelty in the literature. Values of RehK are strongly influenced by the aspect ratio for the case of the short cylinders — for which AR is low. After AR about 9, the curve flattens and the influence of the aspect ratio upon the shedding Reynolds number is very mild. Besides, the paper discusses another very important aspect; the overall stability of the pre-shedding laminar bubble at the base of the body. It is important to stress that the latter study relies on the fact that the boundary layers separation points are fixed.

http://dx.doi.org/10.5028/jatm.v5i3.190 This article presents a study of three different passive devices (spires, screens, and a carpet) separately and in various combinations, to simulate the atmospheric boundary layer (ABL) in a wind tunnel with a short test chamber (465 mm×465 mm×1200 mm). The influence of distances between these devices on the formation of the ABL is established, and optimization of variation of thicknesses of the screens (thin, medium, and coarse) on pressure loss is explored. The results obtained in this work gave support for the analysis of the atmospheric flow and turbulence at Alcantara Launching Center (ALC) in order to launch Brazilian space vehicles under safe conditions. The results show that the "spires" and the thin screen are the devices that require the least area to form an ABL in a test chamber. The physical proximity of two devices (the spires and the medium screen) also influences the size of the ABL formed, which varies from 180 to 200 mm. The power law exponent ranged from 0.12 up to 0.14 after the insertion of a carpet.

Alcântara Space Center (ASC) is the Brazilian gate to the space where rockets of different sizes are launched. At ASC there is a relative topographical variation, coastal cliff, which modifies the atmospheric boundary layer characteristics and can cause interference for operations of rockets. In the present work, a simplified model (mock-up) was studied in a wind tunnel. A scale factor of 1:1000 was used and the atmospheric flow was measured using the hot wire anemometer (HWA) and particle image velocimetry (PIV) techniques. Using of HWA it was possible to calculate values of average wind speed and fluctuations in a set of points of the section of tests that representing the region of the ASC. Through these measures, other meteorological parameters that represent the atmospheric flow, such as the friction velocity (u*), the roughness length (z0) from the logarithmic profile and the alpha exponent (ɑ) of the power law were calculated. With the use of the PIV´s technique, the streamlines and the vorticity fields were obtained and it was noticed that the vorticity generated downwind of the coastal cliff has a strong turbulence (vorticities around 2000 sˉ¹). A rectangular building (simulating the mobile integration tower) was inserted at the mock-up and the downwind turbulence was similar to the one generated by the coastal cliff.

The Alcântara Space Center (ASC) region has a peculiar topography due to the existence of a coastal cliff, which modifies the atmospheric boundary layer characteristic in a way that can affect rocket launching operations. Wind tunnel measurements can be an important tool for the understanding of turbulence and wind flow pattern characteristics in the ASC neighborhood, along with computational fluid dynamics and observational data. The purpose of this paper is to describe wind tunnel experiments that have been carried out by researchers from the Brazilian Institutions IAE, ITA and INPE. The technologies of Hot-Wire Anemometer and Particle Image Velocimetry (PIV) have been used in these measurements, in order to obtain information about wind flow patterns as velocity fields and vorticity. The wind tunnel measurements are described and the results obtained are presented.

Alcantara Space Center (ASC) is the Brazilian gate to the space where rockets of different sizes are launched. At ASC there is a relative topographical variation, coastal cliff, which modifies the atmospheric boundary layer characteristics and can cause interference for operations of rockets. In the present work, a simplified model (mock-up) was studied in a wind tunnel. A scale factor of 1: 1000 was used and the atmospheric flow was measured using the hot wire anemometer (HWA) and particle image velocimetry (PIV) techniques. Using of HWA it was possible to calculate values of average wind speed and fluctuations in a set of points of the section of tests that representing the region of the ASC. Through these measures, other meteorological parameters that represent the atmospheric flow, such as the friction velocity (u(*)), the roughness length (z(0)) from the logarithmic profile and the alpha exponent (alpha) of the power law were calculated. With the use of the PIV's technique, the streamlines and the vorticity fields were obtained and it was noticed that the vorticity generated downwind of the coastal cliff has a strong turbulence (vorticities around 2000 s(-1)). A rectangular building (simulating the mobile integration tower) was inserted at the mock-up and the downwind turbulence was similar to the one generated by the coastal cliff.

The region of the Alcntara Space Center (ASC) presents the formation of Internal Boundary Layer (IBL) generated from a change of surface roughness besides a coastal cliff of 40 m. Numerical simulations, experiments in wind tunnel and observational data were used for this study. The numerical simulations and wind tunnel results matched very well, showing that different inclinations of the coastal cliff influences the presence of a re-circulation zone as well as the turbulence intensity. The different angles do not affect the vorticity that ranged between -1600 and + 300 s(-1), although they cause alterations in the height of the IBL. In the case of the inclinations with angles lower than 90 degrees the region of recirculation becomes more extensive and with the highest values of IBL (of approximately 30 m). An equation of the type ax(b) was fitted to the results from the wind tunnel and values of a=16.9 and b=0.19 were found.