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Wind loads on an azimuthal photovoltaic platform. Experimental study - page 5 / 6

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Fn (ψ=80)

Ft (ψ=80)

Fn (ψ=60)

Ft (ψ=60)

Fn (ψ=30)

Ft (ψ=30)

1.4

1.2

1

Fn, Ft [N]

0.8

0.6

0.4

0.2

0

5

7

9

11 13 15 Wind velocity [m/s]

17

19

21

Fig. 10. Fn, Ft variations

Ψ=70

Ψ=50

Ψ=30

20

18

16

14

Ft/Fn [%]

12

10

8

6

4

2

0

5

7

9

11 13 15 Wind velocity [m/s]

17

19

21

F i g . 1 1 . F t / F n v a r i a t i o n , d e p e n d i n g o n w i n d v e l o c i t y

B. Elevation angle variation

Determinations are performed for the model positioned frontal toward the wind (fixed azimuthal angle ψ = 90°), with change of the tilt angle towards wind direction (altitudinal angle – α = 0 ... 90°, in 10° steps), in the following stages. Loads must be similar with previous determinations since α angle is similar with ψ angle from

the previous determination (angle between wind line and the plane of the platform).

60

40

Ft/Fn [%]

20

0

10

20

30

40 50 Tilt angle

60

70

80

F i g . 1 2 . F t / F n v a r i a t i o n , d e p e n d i n g o n t i l t a n g l e

  • 1.

    Wind velocity is increased in 1 m/s steps in the range of v = 5 ... 20 m/s;

  • 2.

    For each constant wind velocity the components Fdrag and Flift (see fig. 5) of the wind force acting on the model are measured; In this case the lift force Flift is approximately equal to 0, for all determinations because the profile is positioned symmetrical towards the wind line;

  • 3.

    Due to the fact that measurement only offers the Fdrag component of the R total resultant on the platform, the Fn component – normal to the platform is calculated with an assumed approximation (fig. 13) with relations

R

Fdrag sin  

;

n

F R cos  

Fdrag sin  

cos ,

(6)

where φ is the friction angle calculated as

  •  

    arctan

t F

n F

,

the

ratio

t F

n F

being

calculated in the previous determination, depending on tilt angle (see fig. 12).

4.

Due to the fact that the surface of the panel is partially blocking the open of the wind tunnel, the wind velocity at the level of the model is bigger than the wind velocity measured at entering the measurements section. As a result the wind velocity must be corrected for further calculations with relation

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