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: gfisch@iae.cta.br, anacristina@iae.cta.br (2)

National Institute for Space Research, CEP 12227-010, São José dos Campos, Brazil, Email: lubassi@gmail.com,

Ralf.gielow@cpte.inpe.br (3)

University of São Paulo, CEP 13560-970, São Carlos, Brazil, Email: lefraso@icmc.usp.br (4)

Institute of Aeronautical Technology, CEP 12228-904, São José dos Campos, Brazil, Email: girardi@ita.br

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