Wind measurements Sample Clauses

Wind measurements. While generating wind to apply aerodynamic forces on a model, wind properties must be determined accurately at different locations in the working volume: its direction, its average velocity and its variation around its mean value. Wind speed can be written in the three directions as: U = U¯ + u′ V = V¯ + v′ W = W¯ + w′ Vel = ƒU2 + V2 + W2 With the average speed defined as: ¯V¯e¯l = ∑ |VeS| U¯ = ∑ U N V¯ = ∑ V N W¯ = ∑ W N N , with N as the number of samples measured The turbulent intensity is defined as: Iuu = Ivv = Iww = ƒ¯u¯′2¯ ¯V¯e¯l ƒv¯ ′¯2¯ ¯V¯e¯l ƒ¯w¯′¯2¯ ¯V¯e¯l Cup type anemometers or propeller type anemometers measure the average wind speed in one direction. With such devices, even equipped with a vane, the 3D wind direction and turbulent intensity cannot be assessed. The fast variations of velocity are filtered. Hot wire anemometers are not recommended in a humid environment like a test tank. Differential pressure sensors (Pitot type) can measure fast changes in wind speed but are directional sensors. Consequently ultrasonic anemometers are the most usable solution in a lab environment. They allow a three dimensional measurement at a sampling rate up to 30Hz. They are robust and maintenance free. At Ifremer facilities, the wind velocity can reach an average value of 10m/s. To measure turbulence at full power, the anemometer measuring range must be at least 15m/s. The sensor orientation must be adjusted carefully. Getting the wind speed map over the working surface of the wind generator can require a lot of data points. Having numerous anemometers can save a significant amount of time. Figure 2.1: Three 3D ultrasonic anemometers (▇▇▇▇ Windmaster) facing the wind generator for wind characterization. Ifremer wave and wind facilities - 2013