Although turbulence and density variations influence in-field measurements, since this work presents a calibration procedure, we only considered wind tunnel measures at low turbulence levels. For the wind speeds tested, the Reynolds number goes from 1.015 × 10 5 to 4.063 × 10 5. Note that, according to the standard IEC 6, the calibration of a cup-anemometer should be accomplished at low turbulence conditions (axial turbulence below 2%).

The wind tunnel turbulence levels are less than 2%, and the ratio of flow uniformity is high (within 0.2% for x, y, and z axis flows) thanks to several wire meshes, one honeycomb type filter and a convergent nozzle. The uniform main flow in the tunnel is produced by a 5 kW rotating fan with a variable speed drive engine, which provides a flow velocity between 1 m/s and 30 m/s. The cup anemometer was tested in a closed jet-type wind tunnel (see Figure 3), whose testing transversal area is 40 cm by 40 cm.

In other studies, such as those with the target of determining the average flow velocity overestimation, cup anemometer uncertainty is analyzed under time-varying flow, nevertheless, the present study is focused on steady state flows because this is the appropriate procedure for the calibration of cup anemometers.Ĭup anemometer used in the present study. propose, it is difficult to compare those uncertainties to the conventional calibration method performed within a wind tunnel. Although it is possible to assess the measurement variability at a specific site, such as Aquila et al.

Note that in-field calibration has no clear advantages over conventional calibration. The targets of the present study are as follows: (a) show that P w can be obtained using a cup anemometer with a double calibration, so that f r provides Δ p and V, (b) determine the goodness and the uncertainty of the quadratic regression between the wind dynamic pressure and the cup anemometer rotation frequency, (c) quantify and compare the uncertainty of Δ p measurements, with the uncertainty of V measurements obtained according to the conventional method developed in annex F of IEC 6 international standard, and (d) determine if the uncertainty of wind power density calculation decreases when the proposed method, based on dynamic pressure, is applied.īecause cup-anemometers are usually calibrated in wind tunnels, uncertainties calculated from the application of the conventional and proposed calibration are obtained using a wind tunnel. The aerodynamic movement of the cup anemometer is mainly due to drag force, and this force is proportional to air dynamic pressure, which leads us to think that the relationship between air dynamic pressure and cup anemometer rotation frequency is quadratic (see Figure 1b). Hereafter, the cup anemometer used to measure Δ p will be called as “Dynamic Pressure (DYP)-Cup Anemometer”, meanwhile if the anemometer is used to measure V it will be called as “Air Speed (AS)-Cup Anemometer” (see Figure 1). Even more, according to the international standard IEC 6, wind speed is needed to calculate the Annual Energy Production (AEP) and the power coefficient curve ( C P): In the wind energy field, power delivered by wind turbines is calculated from wind speed measurement. The calibration of these devices is growing in importance, since regulations, regarding the determination of potential wind power production, establish a calibration of anemometers before and after each field data collection. Accurate estimations of power curves are required to determine performance and the Annual Energy Production (AEP) of wind turbines. In fact, wind speed metrology is key to assess the energy potential of wind turbines.

In the wind energy field, their use is increasing as the installed wind power capacity does. The use of cup anemometers is widely extended in fields such as meteorology and wind energy production. Current research provides analytical models and numerical studies related to its performance. From the first cup anemometer, invented by Robinson, this device has been investigated and improved. Cup anemometer is a robust and reliable device.

Anemometer calibration