Abstract
A proportionate controller is investigated experimentally for unsteady load alleviation purposes on a 2D wing model with a trailing-edge flap. The controller acts on the velocity of the flaps, and pressure sensors are used to detect the unsteady loads, which are generated by actuating the wing model in a sinusoidal motion. Two different regimes are considered: attached flow and dynamic stall. The influence of actuation frequency and controller time lag is also studied. A reduction of 87.5% in the standard deviation of the lift is obtained for a frequency of 0.2Hz and time lag in the control system of 12ms for attached flow conditions. The reduction of the standard deviation of the lift deteriorates for increased frequency and time lag. The proposed controller is also able to reduce the loads during dynamic stall, although the reduction is smaller, close to 40%, and can negatively affect the aerodynamic damping of the model. The flap actuation is also shown to delay the onset of dynamic stall, by increasing the static stall angle with respect to the case without flap deflection.
Highlights
The increasing demand on wind energy production has resulted in an increase on wind turbine size, as the power extracted scales quadratically with wind turbine size
A reduction of 87.5% in the standard deviation of the lift is obtained for a frequency of 0.2Hz and time lag in the control system of 12ms for attached flow conditions
A simple proportionate controller acting on the velocity of the flap has been tested for load alleviations purposes
Summary
The increasing demand on wind energy production has resulted in an increase on wind turbine size, as the power extracted scales quadratically with wind turbine size. Emphasis should be placed in reducing the weight of the different components of the turbine, as this would reduce the gravitational loads on larger wind turbines. This could result in susceptibility to fatigue damage [2], due to insteady inflow conditions such as wind shear, turbulence or tower shadow wake. Reducing these unsteady loads is necessary if turbines are to become lighter and larger. While a consensus has been reached in using trailing edge flaps as the actuation device, several control and sensing systems have seen successful implementation, with no specific sensor or control architecture proving to be superior for implementation in a Smart Rotor concept [3]
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