Wind Turbine Tip Speed Ratio


One of the key elements affecting the efficacy of wind turbine generators is the tip speed ratio, or TSR.  The rotor of the wind turbine must turn at precisely the right speed.  If the rotor turns too slowly, the wind will move through the spaces between the blades of the rotor without creating any energy. On the other hand, if the rotor moves too quickly, the blades will create a sort of wall, blocking the wind and preventing the wind from catching the blades and being used to create energy. The tip speed ratio must be carefully designed in order to garner as much power from the wind as possible.

As each blade of the rotor turns, it slices through the air and creates turbulence. If the air is still turbulent when the next blade reaches that point, it won’t be able to efficiently create wind power. The tip speed ratio must be adjusted so that the blades do not pass through air that is turbulent.

Calculating Tip Speed Ratio

The tip speed ratio can be calculated by dividing the speed of the tips of the blades by the speed of the wind. For instance, if a wind turbine’s blade tips are turning at a speed of 80 miles per hour and the wind is blowing at 20 miles per hour, then the tip speed ratio would be 80 divided by 20, equaling 4.

Ideal Tip Speed Ratio

The ideal tip speed ratio is not a standard number; the perfect tip speed ratio varies dependent upon the number of blades on the wind turbine rotor. If a wind turbine rotor has fewer blades, it needs to have a higher tip speed ratio in order to harness the maximum amount of energy from the wind. A wind turbine rotor that has only two blades would have an ideal tip speed ratio of about six. A rotor with three blades has an optimum tip speed ratio of about five, and a rotor with four blades has an ideal tip speed ratio of about three. The design of the rotor blades can impact those numbers, though. If a rotor blade has a high efficiency aerofoil design, the ideal tip speed can increase by as much as 25 – 30%. For example, a high efficiency three blade rotor can have an optimum tip speed of up to six or seven.

In cases where a wind turbine uses a tip speed ratio that is too low or the blades are inefficiently designed, the turbine might stall. A tip speed ratio that is too high presents a variety of problems. One risk of an excessively high tip speed ratio is that too much turbulence will be created. This means that the blades will hit turbulent air, which prevents them from effectively generating power. Another risk of excessive tip speed ratio is damage to the wind turbine. A tip speed ratio that is too high will cause stress on the wind turbine and pose a threat of structural damage to the turbine.

If you want to learn more about wind turbines and how you can harness their power to provide your electricity, contact Windpower Technology. We are experts on wind energy for agricultural, commercial, residential, and community use. We will guide you through the development and installation of your wind power system. Just give Windpower Technology a call today to learn more about your options for wind energy.