Active lift control device and method
A lift control device actively controls the lift force on a lifting surface. The device has a protuberance near a trailing edge of its lifting surface, which causes flow to separate from the lifting surface, generating regions of low pressure and high pressure which combine to increase the lift force on the lifting surface. The device further includes a means to keep the flow attached around the protuberance or to modify the position of the protuberance in response to a command from a central controller, so as to provide an active control of the lift between a maximum value and a minimum value.
1. A lift control device for actively controlling lift of a lifting surface when the lift control device is mounted to the lifting surface, the lifting surface being part of a blade of a wind turbine and movable relative to a fluid medium so as to define a leading edge and a trailing edge, the lifting surface also having a pressure surface thereof and a vacuum surface thereof, the leading edge and the trailing edge running along a span of the lifting surface, the trailing edge having a length and defining a longitudinal axis, the lift control device comprising:
a longitudinally disposed vane, the vane having a base and a length;
a set of hinges affixed to the base of the vane;
wherein the base is configured to be mounted to the pressure surface of the lifting surface of the blade of the wind turbine, near the trailing edge of the lifting surface of the blade of the wind turbine, via the set of hinges along the base, the set of hinges defining a pivot about which the vane is rotatable, the vane creating a region of separated flow downstream of the vane, such region having the effect of increasing lift produced by the lifting surface of the blade of the wind turbine when the vane is at a non-zero angle with respect to the pressure surface of the lifting surface of the blade of the wind turbine;
a motor, mountable to the lifting surface of the blade of the wind turbine and coupled to vane, the motor configured to adjust angular orientation of the vane about the pivot, the angular orientation controlling the extent of lift increase produced by the vane; and
a controller, coupled to the motor, and configured to control rotation of the motor and therefore angular orientation of the vane about the pivot, so that the controller controls lift of the lifting surface by controlling angular orientation of the vane.
2. The lift control device according to claim 1 , further comprising: a shaft encoder, coupled to the vane and to the controller, that provides to the controller a signal related to angular orientation of the vane about the pivot; a control line, coupled to the motor, that provides an electrical signal related to torque being produced by the motor, the control line coupled to the controller; wherein the controller is configured to use the electrical signal on the control line to determine a quantity related to wind speed experienced by the vane over the pressure surface and to use the determined quantity to control angular orientation of the vane, as measured via the shaft encoder, so as to adjust lift of the lifting surface in relation to the wind speed.
3. The lift control device according to claim 1 , further comprising a set of fairings mountable to the lifting surface with respect to the vane so as to smooth flow over the vane.
4. The lift control device according to claim 1 , wherein the vane is flexible so as to accommodate flexing of the lifting surface along its longitudinal axis.
5. The lift control device according to claim 4 , wherein the vane includes a plurality of discrete, overlapping elements.
6. The lift control device according to claim 1 , wherein the length of the vane occupies a majority of the length of the trailing edge.