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A STUDY OF THE INTERNAL BOUNDARY LAYER AND TURBULENCE GENERATED AT THE ALCÂNTARA LAUNCHING CENTER
Gilberto Fisch(1), Ana Cristina Avelar(1), Luciana Bassi Marinho Pires (2), Ralf Gielow (2), Leandro Ferreira de Souza (3), Roberto da Mota Girardi (4)
(1) Institute of Aeronautics and Space, Praça Marechal Eduardo Gomes, 50, CEP 12228-904, São José dos Campos,
Brazil, Email: [email protected], [email protected] (2)
National Institute for Space Research, CEP 12227-010, São José dos Campos, Brazil, Email: [email protected],
University of São Paulo, CEP 13560-970, São Carlos, Brazil, Email: [email protected] (4)
Institute of Aeronautical Technology, CEP 12228-904, São José dos Campos, Brazil, Email: [email protected]
ABSTRACT
The region of the Alcântara 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 90º the region of
recirculation becomes more extensive and with the
highest values of IBL (of approximately 30 m). An
equation of the type axb was fitted to the results from the
wind tunnel and values of a=16.9 and b=0.19 were
found.
1. INTRODUCTION
The regime of the winds and the atmospheric turbulence
in the superficial boundary layer have been object of
great interest of Aerospace Meteorology. From its
characteristics are extracted the basic information for
the Research & Development (R&D) of rockets or
analysis of the ambient conditions in situations of non-
successful launchings. Although the wind data usually
are made at meteorological stations, vertical profiles
measurements (like an anemometric tower or mast) give
a detail of the winds. The Reference [1] makes a
complete compilation of the main climatic elements
(specially the winds) at the rockets launchings facilities
in the United States while [2] describes some
experiments using wind tunnel in order to study the
atmospheric conditions at the Space Center of the
Korea. The knowledge of the wind vertical structure
(average profiles and gusts) is important, because the
rockets are projected and constructed to support loads
due to the wind, beyond the fact of its trajectory, control
and guidance are determined by the profile of wind near
the surface.
The region of the Alcântara Space Center (ASC)
presents a peculiar characteristic (coastal cliff) being a
region of abrupt change: from a smooth oceanic surface
for a roughness continental surface, associated with a
relative topographical elevation of 40 m (Fig. 1). In this
place the Brazilian rockets, such as the Satellite
Launcher Vehicle (VLS) and Sounding Rockets
(VSB30) are launched. The rocket launching pad is
located within 150 m from the edge of this coastal cliff.
The wind, initially in balance with the oceanic surface,
interacts with the shrubbery vegetation (average height
of the trees are of 3m), modifying itself with the
formation of an Internal Boundary Layer (IBL).
The objective this work is determines the profiles of
wind, the flow vorticity and the height of the IBL using
different techniques in order to evaluate the turbulence
generated from the coastal cliff in the ASC.
Figure 1. Alcântara Coastal Cliff.
2. DATA SET AND METHODOLOGY
The ASC is located along the coast at the latitude 2° 19'
S and the longitude 44° 22' W and 40 m above sea-
level. The climate presents a precipitation regime
divided in wet period (from January up to June) being
March and April the peak of the rain (higher than 300
mm/month) and a dry period (from July up to
December) with precipitation lower than15 mm/month
[3]. The wind regime possesses a distinct behavior
___________________________________________________________________________________ Proc. ‘19th ESA Symposium on European Rocket and Balloon Programmes and Related Research, Bad Reichenhall, Germany, 7–11 June 2009 (ESA SP-671, September 2009)
between the rainy and dry season. During the wet period
the surface winds are weaker (typically around 4.0 – 5.0
m/s) than during the dry season (winds around 7.0 – 9.0
m/s). This is due to intensification of the sea breeze that
presents its maximum influence during this time
(particularly from September until November). The
wind direction is from the NE at both periods.
Two observational data-sets have been analyzed: an
anemometric tower and a field measurements. A 70 m
tower was instrumented with sensors (Wind Monitor
05103) from R.M Young (Traverse City, USA) at six
levels: 6.0, 10.0, 16.3, 28.5, 43.0 and 70.0 m. The field
campaigns of ECLICA were made in the periods from
April 14 - 24 for the wet season (ECLICLA 1) and
October, 6-16 for the dry season (ECLICLA 2). The
anemometers were located on short masts (points B – 50
m and C- 100 m away from the cliff with heights of 10
and 15 m, respectively). For the ECLICA 2 an extra
anemometer (B2) was added at the height of 4.5 m.
The wind tunnel experiments have been made at ITA
with an open conventional subsonic model. The test
section is square (465 mm x 465 mm) with length of
1200 mm. The devices used for the formation of a
typical atmospheric boundary layer profile (AP) had
been the insertion of spires, a screen (5 x 5 mm) and a
roughness carpet for fine adjustment. The AP was
formed at 1420 mm of the screen and with a height
approximately of 200 mm. The Fig. 2 shows a
schematic of the experimental apparatus used. The air
flow velocity fields were obtained using a 2D PIV
system (Dantec Dynamic, US). The test section flow
was seeded with smoke particles and the instantaneous
images were processed using an adaptive-correlation
software. A 32 pixels × 32 pixels interrogation window
with 50% overlap and moving average validation was
used.
Figure 2. Experimental apparatus used for the
experiments.
The Navier-Stokes equations for 2D incompressible
flows, with constant density and viscosity and
components u and v, respectively in the flow direction x
and vertical direction z, and the vorticity component ωy,
with the inclusion of the immersed boundary condition
through the forcing forces Fx and Fz were used for the
numerical simulations [4]. The boundary conditions at
the inflow are specified based on the Blasius boundary
layer solution; toward the upper boundary the vorticity
is set to decay exponentially to zero; at the outflow the
second derivatives in respect to x of all dependent
variables are set to zero.
Figure 3. Dimensions and schematic representation of
the models experiments.
In order to study the influence of the Mobile Integration
Tower (MTI), a mock-up has been made (with 50 m
height) and insert at a distance of 150 mm (equivalent of
150 m) from the coastal cliff. The IBL height was
determined by finding the position where the vertical
vorticity is null (mathematically ∂wy / ∂z = 0).
3. RESULTS
Tab. 1 presents the data adopted in the experiments and
simulations in order to study the sensitivity of the
system for different inputs. These experiments and
simulations were carried out with different inclination
angles of coastal cliffs and velocities. The maximum
vorticities were obtained in the simulations for the
corresponding Reynolds number (Re) based in coastal
cliff height of 40 m and maximum speed inside the
tunnel.
Fig. 4 shows the wind profile, the stream lines and the
vorticity obtained in wind tunnel experiments with
inclinations of 45, 70, 90, 110 and 135º of coastal cliff.
Notice that for inclinations lower than 90º (Fig. 4a and
4b) there is a formation of eddies at sea level close to
the coastal cliff causing an increase of the IBL height.
In the vorticity graphics (Fig. 4f to 4g), notice that for
the inclination of 45º, a maximum IBL height is equal to
54 m at 100 m of distance. For the inclination of 70º,
this height is 41 m at the same point. For the
inclinations higher than 90º (Fig. 4i and 4j) there is a
reduction of the IBL height e.g. it is 33 m at x = 85 m
for 110º and 25 m at x = 40 m for 135º. It has been also
observed that the geometric structure of the coastal cliff
affects the height of the IBL reaching MTI. For the
coastal cliff with angle of 45º the IBL height at the
position of the MTI is 54 m and for an angle of 135º it is
only 20 m. The wind profile (Fig. 4a to 4e) shows the
formation of a von Karman street vortex after the flow
across the MTI. It is also possible to observe the
formation of recirculation zone at the coastal cliff as
described before. Theoretically, the IBL height is zero
for the usual case of the classical surface roughness
change. However, in this case, the height of coastal cliff
(40 m) introduces a displacement for initial IBL. This
initial height was estimated to be in the range 7-10 m.
The wind vorticity (Fig. 4f to 4j) ranged from -1600 to
300 s-1
. The negative vorticity is associated with the
rotation clockwise of the particles and the positive with
a counter-clockwise rotation. For all cases a vorticity
equal to 300 s-1
is generated by the flow prior to the
MTI and a negative vorticity (-1600 s-1
) is generated at
the coastal cliff and downwind from the MTI.
The code validation was done by comparing the wind
profile simulation results at x = 200 m with the
observations from the anemometric tower, assuming Re
= 2 x 107. The bias (simulated – observed) ranged from
-0.006 to 0.13 m/s and the root mean square error (rms)
ranged from 0.6 to 1.2 m/s. Fig. 5 shows the observed
and simulated wind profile for selected days.
Figure 5. Comparison between observed and simulated
wind profile for April 29, 1998 (a), January 27, 1998
(b), January 24, 2005 (c) and August 02, 2005 (d)
Figure 6 presents the wind vorticity and profiles
obtained for the numerical simulations for an inclination
angle of 90º and Re = 2.0 x 107. The negative values for
the distance represent the flow over the ocean. It can be
notice that the vorticity ranging from 4000 s-1
at the
coastal cliff up to 2000 s-1
at the MTI. The IBL formed
presented a height of 17 m at x = 50 m, 21 m at x = 100
m and 22 m at x = 150 m. The wind profile shows
approximately linear dependence over the ocean and a
logarithmic profile inland. At x = 50 m and x = 100 m it
is possible to observe a formation of a recirculation
region.
Figure 6. Vorticies and Wind Profiles obtained from
numerical simulation.
Fig. 7 shows a comparison of the IBL heights generated
from observations, from the wind tunnel experiments
and from numerical simulations, all with the same Re
(7.5 x 104). It is noticed in Tab. 1 that the maximum
vorticity in this case is very similar, presenting 300 s-1
for wind tunnel experiment and 350 s-1
for numerical
simulation. The semi-empiric expressions derived are
based on representing the IBL height as a type function
axb, where x is the downwind distance of the coast (in
meters), and a and b are empirical constants. The value
of a depends on the change of roughness and thermal
conditions of the surface. Although there is a certain
dispersion of values of a in the literature, the typical
values are between 2 and 5. The other values are
suggested by [5] with the constant a ranges between
0.35 and 0.75 and the coefficient b ranges between 0.1
(smooth surface) and 0.4 (urban areas). It is worthwhile
to notice that this formula can not be used for distances
beyond 1-2 km from the coast, where the growth of IBL
height reaches an asymptotic value [6]. The heights
from the wind tunnel measurements are higher than the
numerical simulation by a factor of 2. The observations
are quite close to the numerical simulations. One reason
for the higher values of the wind tunnel measurements
can be associated with the Re which is relatively low to
describe the atmospheric turbulence.
y = 9.8535x0.1544
R2 = 0.9709
y = 16.947x0.1948
R2 = 0.9259
0
5
10
15
20
25
30
35
40
45
50
0 50 100 150
distance from coastal cliff (m)
heig
ht
(m)
observation numeric simulation experiment
Figure 7. IBL heights computed from observations,
experimental wind tunnel and numerical simulation.
4. CONCLUDING REMARKS
The analyses of the observational data show that the
highest values of windspeed had been concentrated at
point B (distant 50 m from the coastal cliff),
independent of the time. The IBL height has been
estimated to be between the 2 levels of the mast at point
B, indicating a maximum height of 9.0 m.
The different inclination angles of the coastal cliff do
not affect the intensity of vorticity. However, they can
cause alterations in the height of the IBL, influencing a
recirculation region. In the case of the inclinations with
angles lower than 90º the region of recirculation
becomes more extensive and the IBL heights are deeper.
The numerically computed IBL height presented values
closer to the observations than the wind tunnel
experiments.
Analyzing the values obtained for the expression of the
type axb, it can be noticed that the value of a is superior
that ones found in literature, probably due the
turbulence generated for the coastal cliff, while the
value of b is within the range from the literature.
5. ACKNOWLEDGMENTS
The authors would like to thanks the financial support
from the Brazilian Organizations: AEB, CAPES, CNPq
and FAPESP.
6. REFERENCES
1. Jonhson D.L., (1993). Terrestrial environment
(climatic) criteria guidelines for use in aerospace
vehicle development, NASA TM 4511, Huntsville,
US.
2. Kwon K.J., et al., (2003). PIV Measurements on the
Boundary Layer Flow around Naro Space Center.
In Proc. 5th
International Symposium on Particle
Image Velocimetry, Busan, Korea.
3. Fisch G., (1999). Rev. Bras. Meteorol. 14 (1), 11-21.
4. Souza L.F., et al., (2005). Int. J. for Num. Methods in
Fluids 48 (5), 565–592.
5. Arya S.P., Introduction to micrometeorology,
Elsevier – Academic Press, San Francisco, US,
2001.
6. Källstrand B., et al., (1997). Bound. Lay. Meteorol.
85 (1), 1-33.
Figure 4. Wind profiles, stream lines and vorticity obtained in wind tunnel experiments for different geometric
structure of the coastal cliff
Table 1 –Input data and results from the wind tunnel experiments and numerical simulations
Angles Wind Tunnel Experiments Numerical Simulation
EXP Coastal cliff
Inclination Angle (º)
Maximum velocity – V (m/s)
Maximum Vorticity
(s-1)
Re Maximum velocity – V (m/s)
Maximum Vorticity
(s-1)
Re
1 45 28 300 7.5 x 104
7.6 4000
2.0 x 107
2 70 28 300 7.5 x 104 7.6 4000 2.0 x 10
7
3 90 28 300 7.5 x 104 7.6 4000
2.0 x 10
7
4 110 28 300 7.5 x 104 7.6 4000 2.0 x 10
7
5 135 28 300 7.5 x 104 7.6 4000 2.0 x 10
7
6 90 28 300 7.5 x 104 0.03 350
7.5 x 10
4