Fig. 4. Experimental stand and model
Under the measurement section, a force transducer 2 is placed. It can determine two components (Fdrag şi Flift) 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: Fdrag has the same direction with the wind and Flift is horizontal, perpendicular to the wind direction.
For each constant wind velocity the components Fdrag and Flift (see fig. 5) of the wind force acting on the model are measured;
The components relative to the platform of the resultant force are determined: Fn – normal to the platform and Ft – tangential towards the platform surface (fig. 6) with relations
d r a g t d r a g n F F F F
sin Fift cos cos Fift sin
Fig. 5 Directions of the measured components
4. Experimental results
The experimental study developed in two stages:
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);
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).
Azimuthal angle variation
Fig. 6. Forces on the platform for azimuthal angle variation
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.
A Ap sin
where A is the frontal area of the wind turbine and Ap is the area of the panel;
Wind velocity is increased in 1 m/s steps in the range of v = 5 ... 20 m/s;
The force coefficient, without wind velocity correction and the force coefficient with velocity correction result with relations