Salient White Elephant

March 23, 2009

Wobbly Wind Speed and Direction Sensor

Filed under: Wind Turbine Auxilliary Devices — Tags: , , , , — Salient White Elephant @ 5:15 pm

Wobbly Wind Speed and Direction SensorImagine a typical three-cup anemometer. One cup is smaller than the other two, and the other two are the same size. In this case, the rotation speed will vary in a roughly sinusoidal fashion. The speed will be low when the small cup opens up towards the on-coming wind. If, from this position, you rotate the cups 180 degrees, the open end of the small cup will now be in the downwind direction. This will be the position at which the rotation speed is at a maximum. The angular position of the rotating part of the sensor is sampled a number of times per rev. A Fourier Transform is employed to determine the average rotation speed, as well as the phase of the sinusoid relative to some known angular position of the cups. The average rotation speed is proportional to wind speed, and the phase shift reveals its direction. Alternatively,  the amplitude of the sinusoidal variation in rotation speed may be used to calculate the wind speed.

Actuated Variation

In this variation, a small motor drives a rotating paddle at constant rotation speed. Now the instantaneous power consumed by the motor is sinusoidal. The wind speed is a function of the amplitude of the sinusoidal instantaneous power flowing into or out of the motor, and the wind direction is determined from the phase of the sinusoid. Alternatively, the sensor can resemble a miniature Darrieus rotor, with wind speed and direction calculated using similar Fourier techniques.

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