# II - Position of the velocity sensor

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Collection of accurate wind speed data is one of the most problematic elements in conducting wind turbine power performance tests. It allows us to send a signal to the control systems in order to stop the turbine when the wind velocity is too hight, in order to prevent material damage.

The owners of wind farms and turbine manufacturers have shown interest in the use of anemometers placed on the platform for the wind speed data collection, rather than using a meteorological tower upstream of the turbine because of the low cost of this solution.

However, the most significant problem with this practice is that the wind flow is disturbed by the rotor and the nacelle and the wind speed measurements gathered by an anemometer located at the rear of the nacelle does not exactly represent the speed of undisturbed wind upstream of the rotor. This problem can be avoided if the measures can be adjusted.

This second part of the project concerns the modeling of flow at the surface of a wind turbine nacelle in order to find the optimal position for an anemometer.

An optimal position means a spot where the flow is the most uniform, and the less turbulent possible. That would make a correlation between the inlet velocity $V_{\infty}$ and the velocity measured by the anemometer $V_{nacelle}$ with the less residual possible.

Key Parameters:

First we have to sort out the parameters influencing the measurement, which are:

• the nacelle geometry,
• the boundary layer around the nacelle,
• the near wake generated by the rotor and the nacelle,
• the atmospheric boundary layer,
• the pitch angle and the position of the anemometer on the nacelle.

The effect of the nacelle geometry will be studied as a first step (a 2D simulation without the nacelle), then a 3D simulation with the presence of the rotor will be carried out: