Last week we talked about the Aerodynamic Design of a Wind Turbine Blade and Wind Turbine Maintenance. However, there is something that should be expanded on further which incorporates these two important elements!
One of the things rarely discussed about wind turbine blade aerodynamics, is the condition of the blade. For example, the tip speed of a 10m blade at 100rpm is around 360km/hr, so when a blade is moving that fast, it takes very little imperfection to create a large amount of drag. Anyone who has stuck their hand out the window of a car travelling at 120km/hr (75mph) knows the amount of force even on the small area of a hand or finger is significant. When you triple that speed, you’ve increased the amount of drag by a factor of 27 (3 to the power 3). If it takes 10 pounds of force to hold your hand against the wind at 120km/hr, it would take 270 pounds of force at 360 km/hr. Imagine if there are imperfections across the ends of a wind turbine blade that add up to any significant amount of area – nicks, dings, dirt, bird droppings, garbage such as plastic bags or wrappers that may blow in the wind.
Only 100 square centimetres (16 square inches) of roughness and imperfection on the blades could yield 200 pounds (900 newtons) or more of additional drag on the blade – that could rob you of more than 30% of your rated power output! Clean, well kept blades will perform much better than dirty, damaged blades will. The other benefit of a clean blade is that the airflow will remain more laminar across the surface of the blade, leading to less turbulence, this improves the lift characteristics of the blade and helps prevent potentially damaging vibration in the rotor.
As part of yearly maintenance, each wind turbine blade should be examined and repaired if necessary to optimize power output.