a

b

Fig. 4. Experimental stand and model

Under the measurement section, a force transducer 2 is placed. It can determine two components (F_{drag }şi F_{lift}) of the force acting on any profile placed into the wind tunnel. Figure 5 (top view of the profile) shows the directions of the measured components: F_{drag }has the same direction with the wind and F_{lift }is horizontal, perpendicular to the wind direction.

2.

For each constant wind velocity the components F

_{drag }and F_{lift }(see fig. 5) of the wind force acting on the model are measured;3.

The components relative to the platform of the resultant force are determined: F

_{n }– normal to the platform and F_{t }– tangential towards the platform surface (fig. 6) with relations

d r a g t d r a g n F F F F

sin F_{ift }cos cos F_{ift }sin

(2)

## Fig. 5 Directions of the measured components

# 4. Experimental results

## The experimental study developed in two stages:

a.

Azimuthal angle variation; determination of forces acting on the platform and the force coefficient for vertical position of the platform (altitudinal angle α = 90°), with change of the tilt angle towards wind direction (azimuthal angle – ψ = 0 ... 90°, in 10° steps);

b.

Elevation angle variation; determination of force coefficients for a panel positioned frontal toward the wind (azimuthal angle ψ = 90°), with change of the tilt angle towards wind direction (altitudinal angle – α = 0 ... 90°, in 10° steps).

A.

Azimuthal angle variation

Fig. 6. Forces on the platform for azimuthal angle variation

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

Determination is performed for vertical position of the platform (altitudinal angle α = 90°), with change of the tilt angle towards wind direction ψ = 0 ... 90°, in 10° steps, on the following stages.

v_{cor }

## A

v

A A_{p }sin

,

(3)

where A is the frontal area of the wind turbine and A_{p }is the area of the panel;

1.

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

5.

The force coefficient, without wind velocity correction and the force coefficient with velocity correction result with relations