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Wind loads on an azimuthal photovoltaic platform. Experimental study - page 4 / 6

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4 / 6

cf

c f cor

1 2 1 2 F n Apv2 c o r p n 2 v A F ,

,

(4)

(5)

where ρ is the air density.

The numerical values of the parameters involved in the experimental study are: A = 90000 mm2; Ap = 75x75 = 5625 mm2 and ρ = 1.25 kg/m3.

Figures 7 and 8 present the resulted force coefficients, with and without corrections of wind velocity, for sequential ψ angles, depending on wind velocity. The maximum corrected wind velocity is only 6% higher than the measures wind velocity and the difference between

corrected and maximum 12 %.

non-corrected

force

coefficient

is

It can be seen that the force coefficient is decreasing and tending to stabilize for high wind velocity. The stabilized values of the corrected force coefficients cf cor stab have been considered the values obtained for maximum wind velocity and are presented in Figure 9, in comparison with the values recommended by [4] (see Table I) and [6] (see Table II), depending on the tilt angle. Tilt angle ψ is the same with the tilt angle α from Table I and II.

Ψ=90

Ψ=80

Ψ=70

Ψ=60

Ψ=50

Ψ=40

Ψ=30

Ψ=20

Ψ=10

Ψ=0

2

1.8

1.6

1.4

1.2

cf

1

0.8

0.6

0.4

0.2

0

5

7

9

11 13 15 Wind velocity [m/s]

17

19

Fig. 7. Force coefficient without wind velocity correction

Figure 10 presents the variation of the calculated normal and tangential forces, depending on wind velocity, for three different ψ angle.

Figure 11 presents the variation of the calculated ratio b e t w e e n n o r m a l a n d t a n g e n t i a l f o r c e s ( F t / F n ) , d e p e n d i n g

cf_cor

Ψ=90

Ψ=80

Ψ=70

Ψ=60

Ψ=50

Ψ=40

Ψ=30

Ψ=20

Ψ=10

Ψ=0

on wind velocity, for three different ψ angle. It can be seen that this ratio is decreasing and tending to stabilize for high wind velocity. This ratio can be used for determining the tangential component along the surface of the panel (friction force) when the normal force is already determined.

21

1.6

1.4

1.2

1

Fig. 8. Force coefficient with wind velocity correction

0.8

0.6

0.4

0.2

0

5

7

9

11

13

15

Wind velocity_cor [m/s]

17

19

cf Eurocode

cf Titan Tracker

cf

2

1.8

1.6

1.4

1.2

1

0.8

0.6

0.4

0.2

0

0

20

40 60 Tilt angle

80

100

Fig. 9. Force coefficients comparison

Figure 12 presents the variation of the calculated ratio b e t w e e n n o r m a l a n d t a n g e n t i a l f o r c e s ( F t / F n ) , c o n s i d e r i n an average of the values obtained for wind velocity higher than 15 m/s, depending on the ψ angle. g

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