NL2015633B1

NL2015633B1 - Dielectric barrier discharge DBD plasma actuator for an air-foil of a wind turbine or an airplane.

Info

Publication number: NL2015633B1
Application number: NL2015633A
Authority: NL
Inventors: Correale Giuseppe
Original assignee: Univ Delft Tech
Priority date: 2015-10-19
Filing date: 2015-10-19
Publication date: 2017-05-09
Also published as: WO2017069617A1

Abstract

Dielectric barrier discharge DBD actuator for an airfoil of a wind turbine or an airplane, at least comprising a first exposed electrode, a second encapsulated electrode, and a material separating said electrodes and positioned between the first and second electrodes, and wherein the first and second electrodes are staggered with respect to each other, and wherein the actuator is connected or connectable to a sensor or sensors for measuring aerodynamic conditions near the airfoil which provide input to a controller that drivingly connects or is connectable to a power source or power sources of the actuator to induce a plasma in a boundary layer of the airfoil, and comprising a third exposed electrode staggered with respect to the second encapsulated electrode such that the second electrode is positioned between the first and third electrodes, and wherein the power source or power sources are arranged to provide a nanosecond pulse waveform to the first and second electrodes of the actuator and an AC sinus waveform to the second and third electrodes of the actuator.

Description

Dielectric barrier discharge DBD plasma actuator for an airfoil of a wind turbine or an airplane

The invention relates to a dielectric barrier discharge DBD actuator for an airfoil, at least comprising a first exposed electrode, a second encapsulated electrode, and a material separating said electrodes and positioned between the first and second electrodes, and wherein the first and second electrodes are staggered with respect to each other, and wherein the actuator is connected or connectable to a sensor or sensors for measuring aerodynamic conditions near the airfoil which provide input to a controller that drivingly connects or is connectable to a power source or power sources of the actuator to induce a plasma in a boundary layer of the airfoil. The airfoil can be suitably applied in the blades of a windmill or in the wings of an airplane.

The invention also relates to a method to induce a jetstream in a boundary layer of an airfoil, using such a dielectric barrier discharge DBD plasma actuator.

Such a method and dielectric barrier discharge DBD plasma actuator are known from US 2009/0173837 and from US 2010/0004799. US 2009/0173837 discloses that in many instances it is expected that relatively high voltage, narrow width pulses can have a beneficial effect on boundary layers by delaying the transition from laminar to turbulent flow in the boundary layer, and/or by delaying the point at which the boundary layer separates from the surface adjacent to which it flows. Details of representative pulsed discharge actuators are disclosed in AIAA paper 2007 - 941, entitled "Pulsed discharge actuators for rectangular wing separation control" by Sidorenko et al., presented at the 45th AIAA Aerospace Sciences Meeting and Exhibit, Reno, Nevada, January 8 - 11, 2007. US 2009/0173837 further discloses that the narrow width pulses have a relatively high voltage and short duration from about 10 ns to about hundred nanoseconds, and an amplitude of from about 10 kV to about 60 kV. In one embodiment the pulses can be produced at a frequency of about 6 kHz, but in other embodiments the frequency of the pulses can be much higher, for instance from about 10 kHz to about hundred kilohertz. The duty cycle in accordance with which the pulses are produced, that is the percentage of time that the pulses are active or on, can vary from about 10% to about 100%. US 2009/0173837 further discloses in its figure 7 that there can be multiple actuators, i.e. dielectric barrier discharge devices, that are arranged in rows that are oriented at least partially transverse to incoming flow streamlines so as to form a chevron pattern. Accordingly, at least some of the incoming boundary layer flow of the airfoil can be directed with a component transverse to said incoming flow.

The inventor of the instant application has found that the nanosecond pulse waveform applied in US 2009/0173837 is very effective in lowering the density of the boundary layer immediately adjacent to the airfoil and the dielectric barrier discharge DBD actuator, that is to say the density is effectively lowered in the so-called viscous layer that is immediately adjacent to the airfoil. A disadvantage however is that the boundary layer more distant from the airfoil, commonly known as the external layer which is separated from the viscous layer by a buffer layer, is hardly affected by the plasma induced by the actuator. This external layer plays an important role in the amount of drag that the airfoil experiences .

It is an object of the invention to notably reduce the drag of the airfoil and to arrange that the plasma induced by the actuator will at least in part affect the external layer of the boundary layer.

According to the invention it is therefore proposed that the dielectric barrier discharge DBD actuator comprises a third exposed electrode staggered with respect to the second encapsulated electrode such that the second electrode is positioned between the first and third electrodes, and that the power source or power sources are arranged to provide a nanosecond pulse waveform to the first and second electrodes of the actuator and an AC sinus waveform to the second and third electrodes of the actuator. In certain embodiments it may be beneficial to provide the nanosecond pulse waveform to the first and second electrodes simultaneously with the AC sinus waveform to the second and third electrodes, although this is not essential. However, in all embodiments the electrical discharge should happen between the three electrodes at the same time, meaning that the first and third exposed electrodes discharge toward the second covered or encapsulated electrode at the same time. This applies to both waveforms, i.e. the nanosecond pulse waveform and the AC sinus waveform.

Accordingly in the method of the invention a sensor or sensors are used for measuring aerodynamic conditions near the airfoil and used as input to a controller for driving a power source or power sources of the actuator, so as to provide simultaneously power to the first and second electrodes of the actuator in a nanosecond pulse waveform and power to the second and third electrodes of the actuator in an AC sinus waveform.

The invention is based on the surprising thought that the AC sinus waveform that is provided to the second and third electrodes of the actuator will induce a moderate jetstream along the airfoil which will eventually be directed perpendicularly away of said airfoil due to its encountering the normal flow caused by the moving airfoil. This moderate jetstream perpendicularly away of the airfoil moves a low-density air volume that is induced with the nanosecond pulse waveform towards and into the external layer of the boundary layer. The inventor has found that this reduces the drag of the airfoil.

It is remarked that from US 7,380,756 a dielectric barrier aerodynamic plasma actuator apparatus is known which is powered by an AC sinus waveform. There is however no hint, suggestion or any other reason that would induce the skilled person to use this known AC sinus waveform apparatus in combination with a nanosecond pulse waveform apparatus, in the manner as proposed by the invention.

Beneficially a power source is provided to supply additionally an AC sinus waveform to the first and second electrodes of the actuator. This arranges for a further jetstream in a direction parallel to the airfoil and moving from the first to the second electrode, which is opposite to the jetstream caused by the AC sinus waveform applied to the second and third electrodes. Approximately near to the second electrode the two jet streams collide and provide a stronger jet perpendicular to and away of the airfoil into the external layer of the boundary layer. The benefits of the invention are in this way further promoted.

In certain embodiments it may be useful to provide a power source for supplying additionally a nanosecond pulse waveform to the second and third electrodes of the actuator.

The invention will hereinafter be further elucidated with reference to the drawing of an exemplary embodiment of an apparatus according to the invention that is not limiting as to the appended claims.

In the drawing: -figure 1 shows a first embodiment of the dielectric barrier discharge DBD plasma actuator according to the invention; -figure 2 shows a second embodiment of the dielectric barrier discharge DBD plasma actuator according to the invention; and -figure 3 shows an airfoil provided with multiple actuators according to the invention.

Whenever in the figures the same reference numerals are applied, these numerals refer to the same parts.

In figure 1 and figure 2 a part of an airfoil 1 is shown, which is provided with a dielectric barrier discharge DBD plasma actuator. The plasma actuator comprises at an outer surface 2 of the airfoil 1 a first exposed electrode 3, a second encapsulated electrode 4, and a dielectric material 5 positioned between the first 3 and second 4 electrodes. Further it is shown that the first and second electrodes 3, 4 are staggered with respect to each other. The actuator further comprises a third exposed electrode 10 staggered with respect to the second encapsulated electrode 4 such that the second electrode 4 is positioned between the first 3 and third 10 electrodes .

The actuator is connected or connectable to a sensor 6 or sensors for measuring aerodynamic conditions near the airfoil 1 which provide input to a controller 7 that drivingly connects or is connectable to a power source or power sources of the actuator to induce a plasma in a boundary layer of the airfoil 1.

In figure 1 relating to a first embodiment of the actuator of the invention a first power source 8 provides a nanosecond pulse waveform to the first 3 and second 4 electrodes of the actuator, and a second power source 9 provides an AC sinus waveform to the second 4 and third 10 electrodes of the actuator. The nanosecond pulse waveform that is provided to the first 3 and second 4 electrodes induces a plasma near to the airfoil 1 with appreciably diminished density in comparison with the normal air density. The AC sinus waveform that is provided to the second 4 and third 10 electrodes provides a jetstream which is indicated with arrow A that is countercurrent to the normal air flow indicated with arrow B along the airfoil caused by its moving, and which jetstream A eventually departs perpendicular and away from the airfoil 1 upon encountering the airstream indicated with arrow B. The jetstream A departing perpendicular away from the airfoil 1 causes that a low-density air volume which is induced by the nanosecond pulse waveform moves towards and eventually into an external layer of the boundary layer of the airfoil 1, thus reducing the drag of the airfoil.

In figure 2 a second embodiment is shown which differentiates from the embodiment of figure 1 in that the AC sinus waveform is applied not only between the second 4 and third 10 electrodes by power source 9, but also between the first 3 and second 4 electrodes by power source 9'. Likewise the nanosecond pulse waveform is applied not only between the first 3 and second 4 electrodes, but also between the second 4 and third 10 electrodes of the actuator. Particularly the additional AC sinus waveform provided by power source 9' to the first and second electrodes 3, 4 is instrumental to provide in conjunction with the AC sinus waveform provided by power source 9 to the second and third electrodes 4, 10 that a forceful and effective jetstream is provided perpendicular and away from the airfoil 1 directed towards and into the external layer of the boundary layer of the airfoil 1.

Finally reference is made to figure 3, showing an airfoil 1 provided with a plurality of actuators according to the invention, wherein said plurality of actuators are provid ed on the airfoil 1 in a line pattern 11 which is oblique with respect to a normal flow along the airfoil 1, wherein said normal flow is depicted with arrow C.

Although the invention has been discussed in the foregoing with reference to an exemplary embodiment of the apparatus of the invention, the invention is not restricted to this particular embodiment which can be varied in many ways without departing from the invention. The discussed exemplary embodiment shall therefore not be used to construe the appended claims strictly in accordance therewith. On the contrary the embodiment is merely intended to explain the wording of the appended claims without intent to limit the claims to this exemplary embodiment. The scope of protection of the invention shall therefore be construed in accordance with the appended claims only, wherein a possible ambiguity in the wording of the claims shall be resolved using this exemplary embodiment.

Claims

1. Dielectric barrier discharge D3D actuator for an airfoil (1) , at least comprising a first: exposed electrode {3), a second encapsulated electrode (4), which electrodes are separated by a material (5) positioned between the first, and second electrodes (4, 5), and wherein the first and second electrodes (4, 5) are staggered with respect to each other, and wherein the actuator is connected or connectable to a sensor (6) or sensors for measuring aerodynamic conditions near the airfoil (1) which provide input to a controller (7} that drivingly connects or is connectable to a power source or power sources (8, 8', 9, 9f) of the actuator to induce a jetstream in a boundary layer of the airfoil (1), characterised in that it comprises a third exposed electrode (10} stag-gered with respect to the second encapsulated electrode (4} such that the second electrode (4) is positioned between the first and third electrodes (3, 10}, and that the power source or power sources {8, 8', 9, 9'} are arranged to provide a nanosecond pulse waveform to the first and second electrodes (3, 4) of the actuator and an AC sinus waveform to the second and third electrodes (4, 10} of the actuator.

2. Dielectric barrier discharge DBD actuator for an airfoil (1} according to claim 1, characterized in that it is arranged such that the electrical discharge occurs between the three electrodes at the same time, such that the first and third exposed electrodes discharge toward the second encapsulated electrode at the same time.

3. Dielectric barrier discharge DBD actuator for an airfoil (1) according to claim 1 or 2, characterized in that it is arranged that the nanosecond pulse waveform to the first and second electrodes are provided simultaneously with the AC sinus waveform to the second and third electrodes.

4. Dielectric barrier discharge DBD actuator for an airfoil (1) according to any one of claims 1-3, characterized in that a power source (9') is provided to supply additionally an AC sinus -waveform to the first and second electrodes (3, 4} of the actuator.

5. Dielectric barrier discharge DBD actuator for an airfoil (1} according to any one of claims 1-4, characterised in that a power source {8') is provided to supply additionally a nanosecond pulse waveform to the second and third electrodes (4, 10) of the actuator.

6. Method to induce a jetstream in a boundary layer of an airfoil (1), at least using a first exposed electrode (3), a second encapsulated electrode (4), and a material ¢5) separating said electrodes being positioned between the first and second electrodes (3, 4), wherein the first and second electrodes (3, 4) are staggered with respect to each other, comprising applying a sensor (6) or sensors for measuring aerodynamic conditions near the airfoil (1), using the sensor (6) or sensors as input to a controller (7} for driving a power source or power sources (8, 8", 9, 9') of the actuator, characterized by providing a third exposed electrode (10) in a staggered position with respect to the second encapsulated electrode (4) such that the second electrode (4) is between the first and third electrodes (3, 10), and providing power to the first and second electrodes (3, 4) of the actuator in a nanosecond pulse waveform and power to the second and third electrodes (4, 10) of the actuator in an AC sinus waveform,

7. Method according to claim 6, characterized by arranging that the electrical discharge occurs between the three electrodes at the same time, such that the first and third exposed electrodes discharge toward the second encapsulated electrode at the same time.

8. Method according to claim 6 or 7, characterised by providing the nanosecond pulse -waveform to the first and second electrodes simultaneously with the AC sinus waveform to the second and third electrodes.

9. Method according to any one of claims 6-8, characterized by additionally’' supplying an AC sinus waveform to the first and second electrodes (3, 4) of the actuator.

10. Method according to any?· one of claims 6-9, characterized by additionally supplying a nanosecond pulse waveform to the second and third electrodes (4, 10) of the actuator .

11. Airfoil (1) provided with a plurality of actuators according to any one of claims 1-5, characterized in. that, said plurality of actuators are provided oblique on said airfoil with respect to a normal flow along the airfoil.