Small Scale Sensing for Wind Turbine Active Control System
In large wind-turbine parks (farms), gusts, turbulence and interaction of wakes cause significant variation in the wind velocity over rotor blades, with a range of temporal and spatial scales. Arrays of sensors for pressure and wall shear stress at a few key locations, would directly provide data on local wind forces at these locations on the blade surface. Augmented by wind speed field data, wall shear data would be the most directly relevant input for “smart rotor” Active Flow Control (AFC), reducing power intermittency due to localized or large-area boundary-layer separation. Actuators run by a control system with such input could reduce extreme and fatigue loads, power fluctuations, and could help extend the wind speed enve- lope for power extraction. For measuring fluctuations of turbulent wall shear stress, flush-mounted single-hot-film sensors are non-intrusive, but suffer from unaccept- ably large errors caused by significant heat conduction to the substrate. To mitigate this problem, we introduce multi-element guard-heated sensors. Results from our analytical/numerical study show that it is possible to eliminate substrate conduc- tion errors, with careful geometric design of the guard heater. A microfabricated prototype is also presented in this entry.