DE102006028614A1 - Flow surface unit e.g. spoiler, operating method for e.g. aircraft, involves generating electrical power pulses, supplying electrodes with power pulses, and producing plasma in gaseous medium that surrounds electrodes in electrodes - Google Patents

Abstract

The method involves generating electrical power pulses, and supplying electrodes (5a-5c, 6) of plasma producing devices (2) with the power pulses. A plasma in a gaseous medium that surrounds the electrodes is produced in an area of the electrodes of the plasma producing devices, which are supplied with the power pulses. Periodic signals are generated, where the periodic signals has a phase shift. A conveying movement of the plasma is produced along a flow surface unit (1) such as spoiler, by supplying the electrodes with the periodic signals.

Description

TECHNICAL FIELD OF THE INVENTION

The The invention relates to a method of operating a flow area element with several over the flow area element distributed plasma generating devices according to the preamble of the claim 1.

STATE OF THE ART

• – eine Ventilation, insbesondere über perforierte Platten oder Rillen in der Oberfläche des Tragflügels,
• – eine aktive Grenzschichtabsaugung,
• – Konturbeulen in der Oberfläche des Tragflügels,
• – adaptive Oberflächen und/oder
• – mechanische Wirbelgeneratoren

zum Einsatz.In the case of a flight of an aircraft with high subsonic numbers, it may occur during the flow around the wings to form local supersonic areas on the top of the wing. This supersonic area is completed by a compression shock, particularly under off design flight conditions. When passing through the shock entropy of the flow medium increases while at the same time the resting pressure decreases. As a result, a so-called characteristic impedance is caused, which is typical for the Transsonikbereich. Furthermore, the interaction of the compression shock with the boundary layer on the wing can lead to a separation of the boundary layer, which leads to further losses. In addition, flow vibrations can occur. For known measures to influence such a compression shock and its effects come

• A ventilation, in particular via perforated plates or grooves in the surface of the wing,
• An active boundary layer suction,
• Contour bumps in the surface of the wing,
• - adaptive surfaces and / or
• - mechanical vortex generators

for use.

on the other hand also produces an aircraft during a low-flying phase during a flight Takeoffs and a landing unwanted Noise. to Influencing these noise sources while a takeoff and a landing it is known mechanical vortex generators use. In motor vehicles is also an influence the flow conditions via mechanical Elements and flow area elements such as a spoiler.

For the aforementioned different types of vehicles is in the recent past repeatedly the attempt has been made, the flow conditions through the use of plasma generating devices.

• – zu einer Reduzierung einer Turbulenz im Bereich einer Grenzschicht und einer Reduzierung des Turbulenzgrads,
• – zu einer Unterdrückung einer Ausbildung von turbulenten Wirbeln und/oder
• – zur Abschwächung eines Stoßes im Bereich von Stirnseiten des Fahrzeugs

kommen. US 6,570,333 B1 discloses the incorporation of a pair of conductors under insulation of a flat or curved surface of a vehicle that is in the air, such as an aircraft, in the water, such as a ship, or on the ground, such as a motor vehicle or a utility vehicle, emotional. The pair of conductors are subjected to high-frequency energy such that a gaseous medium in the vicinity of the surface forms a plasma. The conductors in this case form electrodes which are spaced apart from one another and oriented parallel to one another. As a result of the formed plasma can lead to a reduction of the flow resistance of the vehicle. An arrangement of the conductors is also possible in small areas of an aircraft in order to change the flow resistance asymmetrically to the longitudinal axis of the vehicle, whereby a non-moving control surface is given. Furthermore, the conductors can be arranged in the region of an input, in the region of the interior or in the outlet region of a turbine, in order to achieve a change in the performance characteristic by influencing the flow. As a result of the formation of the plasma it can

• To reduce turbulence in the area of a boundary layer and to reduce the degree of turbulence,
• To suppress the formation of turbulent vortices and / or
• - To mitigate a shock in the range of front sides of the vehicle

come.

Falls between individual electric pulses the plasma produced is so for one Re-plasma formation requires a re-ionization, which increased Requirements for energy input and training of electrical Would put fields. The electrical energy is at frequencies in the range of 1 MHz and 10 GHz provided. Through the mentioned frequency range can be achieved be that complete Collapse of the plasma between individual pulses of the oscillation is avoided.

The Publication strikes prior to arranging the ladder in a loop, thus forming a field is. Such a field is formed with parallel conductors in the form of substraight pieces, the transverse to the flow and coaxial with the flow are oriented. Another embodiment discloses conductors with several approximately circular, partially overlapping Grind.

It is still out US 6,570,333 B1 It is known to sequentially excite a plurality of downstream electrodes to cause generation of peristaltic plasma waves over the surface of the aircraft. If these plasma waves run from the front to the rear, an acceleration of the plasma in the boundary layer is caused, whereby the flow u. U. can be made rather laminar and the formation of vertebrae is suppressed. In the event that the plasma waves run from back to front, this acts in the boundary layer against the aerodynamic flow, whereby u. U. the flow resistance of the aircraft is increased and a "braking effect" can be caused. Furthermore, by selectively driving the pairs of conductors, the Reynolds number for a transition to a turbulent flow can be raised locally or globally. In the operation of the conductors, the conductors in a pair are subjected to a phase shift of 180 ° with the high-frequency energy.

Out US 6,570,333 B1 It is also known to vary the distance of the conductors across the surface of the aircraft, whereby the density of the plasma can be varied according to local requirements. As an additional use for the formation of the plasma, the document also mentions that formation of ice in the area of a wing can be avoided and ice, which is already on a wing, can be removed. Another embodiment discloses parallel alignment of multiple sections of conductors for processing microelectronic circuits.

US 6,200,539 B1 describes as a side effect of electrodes of a plasma generating device that they exert on the ionized gaseous medium paraelectric electrohydrodynamic (EHD) forces. The document proposes to spatially distribute the electrodes over the flow area element in such a way that, due to the abovementioned forces, movements of the plasma and of the gaseous medium surrounding the plasma are produced, which influence the flow around the flow area element in a suitable manner. In this case, the electrodes are subjected to a single phase of a high-frequency excitation, whereby forces are generated, which are the result of an averaging of attractive and repulsive forces over a high-frequency cycle, which is also referred to as a second-order effect. Furthermore, it is mentioned in the document that much stronger effects should be possible when adjacent electrodes are excited with a multi-phase high-frequency excitation, whereby an electric field is to be generated, which is oriented parallel to the surface of the flow area element. Such an embodiment is also referred to as a "first-order EHD effect". The document is based on the basic idea that the forces exerted on the ionized gaseous medium are significantly determined by the orientation and the geometry of the electrodes and the relative arrangement of adjacent electrodes.

From the pamphlets US 5,414,324 and US 5,387,842 is also a generation of a plasma by excitation of electrodes, here known at a frequency between 5 KV and 100 KHz.

US 5,897,713 relates to the formation of a plasma for the application of a film in a manufacturing process, for example for semiconductors.

Also US 5,797,563 relates to a reduction in the density of a gas surrounding an aircraft in order to reduce the friction and the flow resistance. This is achieved by radiation of electromagnetic waves, which is to be carried out an ionization of the gas. Microwaves are emitted in the region of the front side of an aircraft and along a front contour of a tailplane or above and below a wing of an aircraft.

Also aimed at reducing the density of the gas flowing around the aircraft US 5,263,661 from, in which case a laser is used to heat the gas.

Out US 4,917,335 and US 3,620,484 It is known to produce in front of an aircraft a flame with which the gas flowing around the aircraft is to be heated in order to bring about a reduction in the density.

US 3,446,464 discloses the arrangement of electrodes for generating different electrical potentials at the end edges of aircraft wings.

Further prior art is to influence flow and flow resistance including experimental results
E. Stanewsky, J. Fulker, J. Delery and J. Geissler: Drag Reduction by Passive Shock Control - Results of the EUROSHOCK Project, AER2-CT92-0049 supported by the European Union 1993-1995. Vol. 56 of Notes to Numerical Fluid Mechanics, Vieweg, 1997 ;
Stanewsky, E .; Delery, J .; Fulkner, J .; Matteis, P. de (Eds.): Drag Reduction by Shock and Boundary Layer Control - Results of the EUROSHOCK II Project; supported by the European Union 1996-1999, Springer Verlag, 2002 refer to.

OBJECT OF THE INVENTION

• – der elektrischen Beaufschlagung der Plasmaerzeugungseinrichtungen,
• – des Energieaufwands und/oder
• – einer Wechselwirkung des Strömungsflächenelementes mit einem dieses umströmenden gasförmigen Medium

verbessert ist.The present invention has for its object to propose a method for operating a flow area element, which in terms

• The electrical charging of the plasma generating devices,
• - the energy expenditure and / or
• - an interaction of the flow surfaces Lementes with a flowing around this gaseous medium

is improved.

SOLUTION

The The object of the invention according to the invention with a method with the Characteristics of the independent Patent claim 1 solved. Further embodiments of the method according to the invention arise according to the features of claims 2 to 6.

DESCRIPTION OF THE INVENTION

The The present invention relates to flow area elements which have an influence a flow a gaseous one Medium in the vicinity of the flow area element and / or a Influence of the gaseous Medium in the surrounding area of the flow area element on the flow area element forces applied. Such an influence is based on two effects, namely on the one hand a transformation of the gaseous Medium in a plasma with ionized components, including plasma generating devices on the Flow surface element are distributed as dielectric barrier discharge devices are formed and have electrodes. On the other hand, on the gaseous medium present in the plasma in ionized form forces are exerted by specific generation of electric fields, ultimately an acceleration of the ionized particles and thus an influence on the flow around the flow area element can result.

• a) Es hat sich gezeigt, dass eine Anregung von Elektroden mit elektrischen Leistungspulsen effizienter ist hinsichtlich einer Erzeugung eines Plasmas als eine Anregung der Elektroden mit moderat zeitveränderlichen Signalen wie beispielsweise mit einem sinusförmigen Signal. Dies hat zur Folge, dass für eine Beaufschlagung der Elektroden zur Erzeugung eines Plasmas mit elektrischen Leistungspulsen der zeitliche Abstand der Leistungspulse gegenüber einer Periodendauer eines harmonischen Signals u. U. vergrößert werden kann und/oder die Energie und Leistung der elektrischen Leistungspulse gegenüber der Energie und Leistung eines harmonischen periodischen Signals reduziert werden kann.
• b) Andererseits bedeuten impulsartige Beaufschlagungen der Elektroden stark zeitvariante elektrische Impulse zwischen benachbarten Elektroden, die damit stark veränderliche Kräfte auf ein erzeugtes Plasma ausüben können. Um eine gezielte Beschleunigung der ionisierten Teilchen des Plasmas zu erzeugen, ist somit eine impulsartige Anregung nicht zwingend erforderlich – u. U. kann sogar mit einem zwischen benachbarten Elektroden ausgebildeten elektrischen Feld mit konstantem Gradienten eine zumindest für ein zeitliches Teilinterval konstante Kraft vorteilhaft sein für eine Beschleunigung der geladenen Teilchen in eine gewünschte "Förderrichtung".

The invention is further based on the recognition that the requirements for an electrical application of electrodes in the region of the flow area element to bring about the two aforementioned effects are different:

• a) It has been found that excitation of electrodes with electric power pulses is more efficient in generating a plasma than excitation of the electrodes with moderately time varying signals, such as a sinusoidal signal. This has the consequence that for applying the electrodes for generating a plasma with electric power pulses, the time interval of the power pulses with respect to a period of a harmonic signal u. U. can be increased and / or the energy and power of the electric power pulses with respect to the energy and power of a harmonic periodic signal can be reduced.
• b) On the other hand, impulse-like exposures of the electrodes represent strongly time-variant electrical impulses between adjacent electrodes, which can thus exert highly variable forces on a generated plasma. In order to generate a targeted acceleration of the ionized particles of the plasma, thus a pulse-like excitation is not absolutely necessary - u. For example, even with a constant gradient electric field formed between adjacent electrodes, a force constant at least for a partial time interval can be advantageous for accelerating the charged particles in a desired "conveying direction".

The resulting conflict of objectives is for the US 6,200,539 B1 and US 6,570,333 B1 known method solved in that a high-frequency signal is selected, which is sufficiently dimensioned to bring about ionization. An influence of the applied forces on an electric field is brought about by arrangement, asymmetrical distances and orientation of the neighboring electrodes, s. US 6,200,539 B1 , Thus, an electrical signal is suitably adapted to both the generation of the plasma and the advantageous design of the electric field.

• – Einerseits werden elektrische Leistungspulse erzeugt, mit denen Elektroden der Plasmaerzeugungseinrichtungen beaufschlagt werden. Die Leistungspulse sind optimiert hinsichtlich einer Erzeugung eines Plasmas.
• – Daneben werden periodische Signale erzeugt, deren Energie und Leistung u. U. unter dem Niveau liegen kann, welches zur Erzeugung eines Plasmas erforderlich ist. Die periodischen Signale werden Elektroden zugeführt, die im Umgebungsbereich des erzeugten Plasmas angeordnet sind. Hierbei kann es sich um Elektroden handeln, die auch zur Erzeugung eines Plasmas dienen, oder um zusätzliche Elektroden, die ausschließlich zur Ausübung von Kräften auf ionisierte Teilchen dienen. Durch Beaufschlagung dieser Elektroden wird eine Förderbewegung des Plasmas entlang dem Strömungsflächenelement erzeugt. Damit kann das periodische Signal gezielt auf eine Optimierung der Förderbewegung ausgelegt werden, ohne dass die Optimierung an die Erfordernisse für eine Erzeugung eines Plasmas angepasst werden muss.

According to the invention, two qualitatively different signals are used to produce the previously described desired effects a), b), which can each be optimized for one of the desired effects:

• On the one hand electrical power pulses are generated, which are applied to electrodes of the plasma generating devices. The power pulses are optimized for generation of a plasma.
• - In addition, periodic signals are generated whose energy and power u. U. may be below the level required to produce a plasma. The periodic signals are applied to electrodes disposed in the surrounding area of the generated plasma. These may be electrodes which also serve to generate a plasma, or additional electrodes which serve exclusively for exerting forces on ionized particles. By applying these electrodes, a conveying movement of the plasma along the flow area element is generated. Thus, the periodic signal can be designed specifically for optimizing the conveying movement, without the optimization having to be adapted to the requirements for generating a plasma.

While according to US 6,200,539 B1 for periodic signals, an electric field has been generated primarily by an asymmetrical arrangement of a plurality of electrodes of the same potential, proposes the invention that the periodic signals are supplied to the electrodes for generating a conveying movement with a phase shift. As a result of the phase shift, regardless of a position and / or orientation of the electrodes, an electric field may arise whose magnitude may depend on the amplitude of the periodic signal, the phase shift and the distance between the electrodes. Thus, in addition to influencing the resulting electric field across the arrangement and orientation according to US 6,200,539 B1 given by the phase shift further influencing possibilities for the conveying movement as a result of the inventive design.

The inventive phase shift can be actively generated by a suitable power supply, so that the power supply has several periodic signals with different, defined phase shifts brought about. It is also conceivable that a central, generated by a power supply periodic Signal over different electrical components targeted with a phase shift is provided, wherein the components in a respective one electrode and the power supply having circuit interposed are. Possible is that both the periodic signal and the electrical Power pulses provided by the same electrical power supply become. Alternatively you can the periodic signals and the power pulses from separate power supplies to be provided.

A is particularly simple embodiment of a periodic signal according to a Further development of the method according to the invention given when these are called harmonic signals (sinusoidal signals) are formed. For example, such signals can by Oscillators are provided and / or amplified.

The Electrodes can with the interposition of a dielectric rectilinear or arbitrarily curved or with partial straight sections in the area of a surface extend. According to one first embodiment are the electrodes to which the power pulses are applied, and the electrodes that apply the periodic signals be, at least in some areas approximately perpendicular, in particular with an angle between 80 ° and 100 °, to each other oriented. This has the consequence that a parallel to the plasma field applied to the power pulses by the electrodes applied with the periodic signals approximately in the direction of its longitudinal extent with powers is charged.

In the case, that an exercise of forces transverse to the longitudinal extent desired of such a plasma field is, this can be produced in a particularly simple way, that the electrodes subjected to the power pulses and the at least with the periodic signals acted upon electrodes in subareas approximately are oriented parallel to each other, in particular at an angle from -10 ° to + 10 °.

A particularly compact embodiment of the method according to the invention and the flow area element used in the process arises when for an application of power pulses to generate the plasma and an application of a periodic signal for generation the conveyor movement the same Electrodes are used. This allows the number of electrodes reduced, in particular halved. This embodiment of Invention means that the electric power pulses and a periodic signal are superimposed to a single signal, with which then the electrodes are acted upon. This has the consequence that the Field due to the periodic signal immediately in the area acts, in which the plasma is generated, namely in the surrounding area of the same Electrode.

U. U. can over the choice of a phase shift of the periodic signal from adjacent ones Electrodes the size of the electrical Field between the electrodes are affected. On the other hand results a change of the electric field as required the distance of the adjacent electrodes. A particularly homogeneous Field in the area of the surface a flow area element also over several adjacent, acted upon by periodic signals electrodes results when the electrodes are approximately equidistant from each other are and the phase shifts between adjacent electrodes each approximately are constant.

Advantageous developments of the invention will become apparent from the claims, the description and the drawings. The advantages of features and of combinations of several features mentioned in the introduction to the description are merely exemplary and can come into effect alternatively or cumulatively, without the advantages having to be achieved by embodiments according to the invention. Further features are the drawings - in particular the illustrated geometries and the relative dimensions of several components to each other and their relative arrangement and operative connection - refer. The combination of features of different embodiments of the invention or of features of different claims is also possible and deviates from the chosen relationships of the claims here with excited. This also applies to those features which are shown in separate drawings or are mentioned in their description. These features can also be combined with features of different claims. Likewise, in the claims listed features for further embodiments of the invention can be omitted.

BRIEF DESCRIPTION OF THE FIGURES

in the The invention is described below with reference to the figures preferred embodiments further explained and described.

1 shows a flow area element with plasma generating devices in a side view.

2 shows the flow area element according to 1 in a top view.

3 shows a further embodiment of a flow area element in a plan view.

4 shows a further embodiment of a flow area element in a plan view.

5 shows a schematic block diagram of a method according to the invention for operating a flow area element.

6 shows a schematic block diagram for an alternative method according to the invention for operating a flow area element.

DESCRIPTION OF THE FIGURES

A illustrated in the figures flow area element 1 finds use, for example, in a vehicle which may be an aircraft, land vehicle, watercraft, spacecraft or as a vehicle for a combination of the aforementioned purposes. Alternatively, the flow area element 1 Use find in through-flow line systems, a medical management system, a pipeline, an exhaust pipe, a turbine, a conveyor for the treatment of a surface including a plasma cleaning, sterilization, a heating system, a ventilation system, an air conditioner u. ä. The flow area element 1 is used to influence a flow, avoiding or causing vortexes, creating a countercurrent flow, delayed or accelerated flow, or deliberately inducing or reducing flow-induced forces on the flow surface element. In the case of a use of the flow area element in a vehicle, the vehicle preferably moves in the range of low speeds from 50 km / h up to supersonic speeds in the transonic or supersonic range. Furthermore, the use of a flow surface element for an aircraft in any layers of air through to the use of a reentry aircraft (shuttle) is conceivable.

In the flow area element 1 are several plasma generating devices 2 through a dielectric 3 separated from each other. By means of the plasma generating device 2 may be the flow area element 1 in the area of the surface 4 flowing around the gaseous medium locally or along the extension of the plasma generating device 2 be converted into a plasma with ionized particles. For this purpose, all of the aforementioned plasma generating devices according to the prior art can be used. In particular, the plasma generating device generates a movement of the charged plasma particles, that is, ions or electrodes, which interact with the flow surface element. For example, the charged plasma particles can affect the neutral particles of the flow, so that their speed is changed, in particular the direction of the speed is changed, and / or the amount of speed is increased or decreased. Furthermore, it is possible that by the plasma generating device 2 the boundary layer is influenced, for example, the thickness of the boundary layer is changed. As explained above, via the plasma generating device 2 the flow in the area of the flow area element 1 accelerated or slowed down. Also a qualitative change of the flow in the area of the flow area element 1 is possible by deliberately generating a vortex or a turbulent flow is induced or the formation of vortices or a turbulent flow is selectively prevented. It has been shown that a use of a plasma generating device 2 in the region of a flow area element 1 is possible without the outer contour of the flow area element must be changed mandatory. As a result, the use of the plasma generating device 2 as an "add-on" possible without a re-interpretation of the flow area element is required. The plasma generating device 2 may be formed as a so-called "dielectrically impeded discharge device". Such discharge devices are also referred to in the literature as "dielectric barrier discharge". In the context of the present invention, the dielectrically impeded discharge device is understood to mean a device in which at least one dielectric, which forms a barrier, is interposed between two electrodes and the flow of the flow surface element. The dielectric may be a sheath of the Acting electrode, which is integrated, for example, in the flow surface element in the region of the surface thereof.

For the in 1 and 2 illustrated embodiment of the flow area element 1 extend alternately from opposite end faces of the flow area element electrodes 5 in the area of the surface 4 , Transverse to these extend from a side surface of the flow area element 1 electrodes 6 located inside the flow area element 1 encased in the dielectric 3 , are arranged. Notwithstanding the simplified representation according to 1 can the electrodes 5 in the surface 4 be integrated with a smooth outer contour. The electrodes 5 . 6 are each aligned in a straight line, with the electrodes 5 (as well as electrodes 6 ) are each oriented parallel to each other and are arranged equidistant from each other.

For the in 3 illustrated embodiment are rectilinear electrodes 7 oriented parallel to each other and equidistant in the surface 4 the flow area element 1 integrated. Electrodes connected to the ground 8th are in the dielectric 3 integrated and parallel to each other and to the electrodes 7 oriented, the electrodes 8th off-center between adjacent electrodes 7 are arranged.

For the in 4 illustrated embodiment of a flow area element 1 owns these electrodes 5 , Electrodes 6 and grounded electrodes 8th , which are each arranged parallel to each other at equal distances from each other, wherein the electrodes 6 and 8th off-center between two adjacent electrodes 5 are arranged.

For the inventive method are in a power supply 9 periodic signals 10a . 10b . 10c , in particular harmonic signals, generated, s. 5 , The periodic signals 10a . 10b . 10c each have a phase shift, which may have the same or different amounts. In particular, the signals are um
signal 10a S _10a = S _max sin (t),
signal 10b : S _10b = S _max sin (t + Δφ)
signal 10c : S _10c = S _max sin (t + 2Δφ)

The signals 10a . 10b . 10c be the electrodes 5a . 5b . 5c supplied, s. 1 and 2 respectively. 4 ,

Another power supply 11 generates electrical power pulses 12 with or without phase shift to the electrodes 6a . 6b . 6c be supplied, s. 1 and 2 respectively. 4 , Alternatively, the power supplies 9 and 11 be formed by a central power supply.

For the in 6 illustrated variant of the method according to the invention are the periodic signals 10a . 10b . 10c with the electrical power pulses 12 to the superimposed signals 13a . 13b . 13c superimposed. The superimposed signals 13a . 13b . 13c be the electrodes 7a . 7b . 7c supplied, s. 3 ,

In the event that, as in 3 and 4 shown connected to ground electrodes 8th are provided, a pulse operation for generating a plasma by alternately connecting the electrodes 8th and 6 be brought about.

When rough guideline for a frequency of the power pulses may be about 100 kHz (± 10%, ± 20%) be specified for which a gross efficiency maximum experimentally proven can.

1

Flow surface element

2

Plasma generating device

3

dielectric

4

surface

5

electrode

6

electrode

7

electrode

8th

electrode

9

power supply

10

periodic signal

11

power supply

12

electrical power pulses

13

layered signal

Claims (6)

Method for operating a flow area element ( 1 ) with several via the flow area element ( 1 ) distributed plasma generating devices ( 2 ), which are designed as dielectrically impeded discharge devices and electrodes ( 5 . 6 . 7 . 8th ), characterized in that a) electrical power pulses ( 12 ), b) electrodes ( 6 ; 7 ) of plasma generating devices ( 2 ) with the power pulses ( 12 ), c) in the region of the electrodes ( 6 ; 7 ) of plasma generating devices ( 2 ) with the power pulses ( 12 ), a plasma in one of the electrodes ( 6 ; 7 ) ambient gaseous medium is generated, d) periodic signals ( 10a . 10b . 10c ), wherein at least two periodic signals ( 10a . 10b . 10c , ...) have a phase shift, e) two electrodes ( 5a . 5b . 5c ; 7 ) arranged in the surrounding area of the generated plasma, phase-shifted periodic signals ( 10a . 10b . 10c , ...), f) by the application of the electrodes ( 5a . 5b . 5c ; 7 ) with the phase-shifted periodic signals ( 10a . 10b . 10c ) a conveying movement of the plasma along the flow area element ( 1 ) is produced. Method according to Claim 1, characterized in that the periodic signals ( 10a . 10b . 10c ) are formed as harmonic signals. Method according to claim 1 or 2, characterized in that with the power pulses ( 12 ) acted upon electrodes ( 6a . 6b . 6c ) and with the periodic signals ( 10a . 10b . 10c ) acted upon electrodes ( 5a . 5b . 5c ) are oriented approximately perpendicular to each other. Method according to claim 1 or 2, characterized in that with the power pulses ( 12 ) acted upon electrodes ( 6a . 6b . 6c ) and with the periodic signals ( 10a . 10b . 10c ) acted upon electrodes ( 5a . 5b . 5c ) are oriented approximately parallel to each other. Method according to one of claims 1, 2 and 4, characterized in that the same electrodes ( 7 ) with both power pulses ( 12 ) as well as with a periodic signal ( 10a . 10b . 10c ). Method according to one of the preceding claims, characterized in that adjacent to periodic signals ( 10a . 10b . 10c ) acted upon electrodes ( 5a . 5b . 5c ) are approximately equidistant from each other and the phase shifts (Δφ, 2 Δφ, 3 Δφ, ...) between adjacent electrodes ( 5a . 5b . 5c ) are each approximately constant.