Patent Application
20200369380
The present invention pertains to a method for active flow control, a flow body, and an aircraft.
Although applicable for any kind of fluid flow fields or structures subject to a fluid flow, the present invention and the corresponding underlying problems will be explained in further detail in conjunction with aircrafts.
Flow bodies such as wings or control surfaces of an aircraft typically require a fully attached flow to work properly in a variety of flow conditions. For example, flow surfaces of wings of an aircraft are optimized for high flow velocities that occur during a cruise flight phase in high altitudes. However, during starting and landing phases, the wings are required to provide lift at low flow velocities and, typically, are positioned with a high pitch angle. In order to meet these requirements and to prevent stall or flow separation in particular at high pitch angles, todays aircraft wings are equipped with high-lift devices, e.g. slats and flaps arranged at a leading edge of the wing, the slats being extendable from the leading edge allowing an overflow of air from a pressure side of the wing to a suction side of the wing, wherein the overflowing air energizes the flow on the suction side and thereby prevents flow separation. Further, wings comprising so called Krueger flaps or so called droops are known. This type of flap is arranged at a leading edge of the wing and is movable so as to locally reduce an angle of attack of the fluid flow.
Moreover, fluidic actuators may be employed for preventing flow separation. Typically, fluidic actuators are coupled to openings in the flow surface and configured to eject continuous or pulsed jets into the flow flowing over the flow surface in order to energize the boundary layer of the flow to prevent flow separation.
EP 3 144 221 A1 describes a cooperative actuator system with first row of actuators and a second row of actuators positioned downstream of the first row, the actuators being configured to eject pulsed air flow. The first row introduces a first flow structure, i.e. a vortex structure, into a fluid flow flowing over a flow surface and the second row of actuators is controlled based on a measured propagation of the first flow structure so as to amplify the first flow structure.
Aspects of the invention may provide improved, in particular robust and reliable solutions for active flow control.
According to a first aspect of the invention, a method for active flow control of a fluid flow that flows along a flow surface is provided. The method comprises generating a first local velocity field in the fluid flow by introducing a first vortex structure, for example a horseshoe vortex, into the fluid flow by means of a first flow control actuator coupled to a first actuation site of the flow surface, and introducing a second vortex structure, in particular a horseshoe vortex, into the first local velocity field by means of a second flow control actuator coupled to a second actuation site of the flow surface located downstream of the first actuation site, when a head vortex of the first vortex structure has propagated with the fluid flow downstream the second actuation site.
According to a second aspect of the invention a flow body system is provided. The flow body system comprises a flow body defining a flow surface. The flow body comprises a group of first flow control actuators coupled to the flow surface at a row of first actuation sites, wherein the first actuation sites are spaced to one another in a first direction. The first flow actuators are configured to generate first vortex structures and corresponding first local velocity fields in a fluid flow flowing along the flow surface along a second direction which extends transverse to the first direction. The flow body further comprises a group of second flow control actuators coupled to the flow surface at a row of second actuation sites and configured to generate second vortex structures and corresponding second local velocity fields in the fluid flow, wherein the second actuation sites are spaced to one another in the first direction and being positioned spaced to the group of first actuation sites in the second direction extending transverse to the first direction. The system further comprises a controller communicatively connected to the first and second flow control actuators. The controller is configured to control the first flow control actuators in accordance with a method according to the first aspect of the invention. That is, the controller is configured to control the first actuators to generate a first local velocity field in a fluid flow flowing along the flow surface along the second direction by introducing a first vortex structure into the fluid flow, and to control the second flow control actuators to introduce a second vortex structure into the first local velocity field, when a head vortex of the first vortex structure has propagated with the fluid flow downstream the row of second openings.
According to a third aspect of the invention, an aircraft comprising a flow body system according to the second aspect is provided. The flow body may form a wing of the aircraft, a part of the wing, a vertical stabilizer, a horizontal stabilizer, or another structure of the aircraft subject to a fluid flow.
It is one of the ideas of the present invention to generate a first vortex structure in a fluid flow, e.g. a horseshoe vortex having a head vortex and two lateral longitudinal vortices, at a first location, and to generate a second vortex structure, e.g. another horseshoe vortex, at a second location downstream of the first location somewhat after the head vortex of the first vortex structure has passed the second location. By introducing the first vortex structure, which may for example be done by continuously or pulsed ejecting a high velocity fluid jet from a slit shaped first opening into the boundary layer of the fluid flow, a local velocity field is generated upstream of the head vortex which propagates downstream with the fluid flow. The first actuators thus energize the boundary layer of the outer, free stream flow, e.g. by blowing out a jet of fluid, and create a local high-velocity field where the velocity is higher than in the free stream flow or at least higher than the velocity in the boundary layer of the freestream flow. Thereby, the fluid flow is energized within the local velocity field and, hence, comprises a velocity that is greater than in the surrounding boundary layer. When the head vortex of the first vortex structure has passed the second location, e.g. a second opening downstream of the first opening, the local velocity field of the first vortex structure is still present upstream and downstream of the second location and, thus, a second vortex structure can be generated in the energized local velocity field, e.g. by ejecting a high velocity fluid jet from the slit shaped second opening into the local velocity field.
For generating the first and second vortex structures, first and second flow control actuators may be used, wherein one flow control actuator is coupled or connected to at least one actuation site. The flow control actuators may for example be configured to eject a control fluid through openings in the flow surface and comprise corresponding flow control structures such as nozzles, diffusors, flaps, valves, membranes, or similar structures configured to control a flow of a fluid. In this case, the flow control actuators may be coupled to a source of high pressure fluid, e.g. a reservoir or a pressure generator such as pump or compressor. It is also possible, e.g. in an aircraft, to connect the actuators to an opening forming a stagnation point, for example an opening provided at a leading edge of a wing. Alternatively, the first and second actuators may also be realized as plasma actuators. In this case, an electrode arrangement may be positioned at each actuation site, wherein the electrode arrangements are connected to an electric voltage source and configured to generate plasma between a pair of asymmetric electrodes. Generally, the first and second flow control actuators may also form a common structure, e.g. in the form of a fluidic oscillator.
For timing and activating the actuators, a controller may be used, e.g. a micro controller or, generally, a processing unit configured to generate control commands based on which the flow control actuators are activated, e.g. to generate plasma or to eject fluid. The controller may comprise a non-volatile data memory, such as a flash memory or similar, and a processing unit, such as a CPU, an FPGA, an ASIC, or similar. The controller is communicatively coupled or connected to the flow control actuators, e.g. via a data connection such as a bus system. The controller may comprise an input interface for receiving data, e.g. data representing state variables of the fluid flow, such as velocity, angle of attack, and similar. Optionally, the controller is configured to generate control commands based on the data received at the input interface.
It is one of the advantages of the present invention that the second vortex structure is introduced into the local high-velocity field of the first vortex structure since, thereby, a gradient between the second vortex structure and the fluid of the fluid flow is reduced. In other words, the second vortex structure is introduced in an energized local flow field with high velocity instead of being introduced into the boundary layer of the free stream flow. Thereby, the second vortex structure is highly energized and, consequently, remains stable and energized over a long distance downstream of the second opening. Thereby, the second vortex structure efficiently energizes the boundary layer of the fluid flow over a long distance and, hence, efficiently prevents flow separation.
Another advantage lies in that the method is robust with respect to varying flow conditions. This is mainly based on the effect that the first vortex structure when propagating downstream with the fluid flow laterally grows or widens. Thereby, the second vortex structure can be easily placed within the first local velocity field. Since the first local velocity field, based on a duration of activation of the first actuator, e.g. a duration of ejecting control fluid at the first ejection site, comprises a certain expanse in the flow direction of the fluid flow ejecting control fluid at the second ejection site or openings can be timed with relatively high tolerances while the second vortex structure is still reliably placed within the first local velocity field. Consequently, there is not necessarily a need to measure propagation of the head vortex of the first vortex structure but the second flow control actuators may be activated by the controller based on internal controller data, e.g. after a predefined lapse of time after activating the first flow control actuators. Thus, the method and the fluid body is highly fail safe.
Related to aircrafts, the flow body may form a wing or part of a wing or a control surface. One advantage of the present invention is that slats possibly can be omitted or at least locally replaced when the flow body forms part of the wing, in particular a leading edge of the wing in the region of a slat end at the outer wing, or in the region of an engine-wing coupling or at the leading edge of a trailing edge flap.
It should be understood that features and advantages described in connection with one aspect of the invention are also disclosed for the other aspect of the invention and vice versa. In particular, the flow body system may perform the method steps of the method according to the first aspect of the invention.
According to an embodiment of the method, the method further comprises introducing a third vortex structure into the first local velocity field by means of a third flow control actuator coupled to a third actuation site of the flow surface located downstream of the second ejection site, when the head vortex of the first vortex structure has propagated with the fluid flow downstream the third ejection site. For example, the first and the second vortex structures may be generated by simultaneously activating the second and third actuators, e.g. to eject control fluid at the second and third actuation sites. However, it is also possible to activate the third actuator after starting activating the second actuator. By introducing second and third vortices structures into the local high-velocity field at consecutive locations, a plurality of consecutive high energized vortices can be generated which further helps to prevent flow separation.
According to one embodiment, the third vortex structure is introduced into the first local velocity field after a second local velocity field generated by introducing the second vortex structure has propagated downstream the third actuation site. Hence, the second actuator may be activated to generate the second vortex structure and a corresponding second local high-velocity field only for a short period of time. The first actuator may be kept activated during activation of the second actuator and after deactivation of the second actuator. When the second local high-velocity field has propagated downstream the third actuation site, the third actuator is activated, e.g. to eject control fluid. Alternatively, the third vortex structure may be introduced into the first local velocity field before a head vortex of the second vortex structure has reached the third actuation site. In both alternatives, a series of consecutive, highly energized vortices may be produced by merely shortly activating the second and third actuators, that is, with short duty cycles. Thereby, the vortices can be efficiently generated.
According to another embodiment, the method further comprises introducing a third vortex structure into a second local velocity field generated by introducing the second vortex structure, the third vortex structure being introduced by means of a third flow control actuator coupled to a third actuation site of the flow surface downstream of the second actuation site, when a head vortex of the second vortex structure has propagated with the fluid flow downstream the third actuation site. Similar to the first vortex structure, also the second vortex structure may be a horseshoe vortex which defines a second local field of high velocity upstream of its head vortex. When a further, third vortex structure is introduced in said second local velocity field at a location downstream of the second actuation site, e.g. by ejecting control fluid through third openings, the third vortex structure is stabilized and highly energized and, hence, may travel downstream over a long distance which further helps to prevent flow separation.
According to one embodiment, the third vortex structure may be introduced into the second local velocity field after the first local velocity field has propagated downstream the third actuation site. That is, the first actuator may be active over a first period of time to generate the first local velocity field into which the second vortex structure is placed at the second actuation site. When the first actuator is deactivated, the first local velocity field propagates downstream and passes the second and third actuation sites, e.g. a second and a third opening of the flow surface. The second actuator is still active and generates a second local velocity field, e.g. by ejecting fluid through a second opening of the flow surface. According to one embodiment, the third vortex structure is introduced at a point of time when the first local velocity field has already passed the third actuation site so that the third vortex structure is placed into the second local velocity field. Alternatively, the third vortex structure may be introduced into the second local velocity field when the first local velocity field is still present upstream and downstream of the third actuation site so that the third vortex structure is placed into the second local velocity field which superimposes the first local velocity field.
According to one embodiment, the method further comprises introducing a fourth vortex structure into the fluid flow by means of the first flow control actuator, e.g. by ejecting control fluid at the first actuation site, wherein the third flow control actuator continuously generates a third local velocity field, e.g. by continuously ejecting control fluid, until a head vortex of the fourth vortex structure has propagated downstream the third actuation site with the fluid flow. For example, control fluid may subsequently ejected at the first, the second, and the third actuation sites or openings in a pulsed fashion, wherein control fluid is ejected at the first actuation site over a predefined first period of time, wherein control fluid is ejected at the second actuation site over a predefined second period of time when the head vortex of the first vortex structure has passed the second actuation site, wherein control fluid is ejected at the third actuation site over a predefined third period of time when the head vortex of the second vortex structure has passed the third actuation site, wherein control fluid is ejected at the first actuation site again after the predefined first period of time has ended and after a predefined delay to generate a fourth vortex structure, optionally after starting ejection of control fluid at the third actuation site, and wherein the predefined third period of time is sufficiently long for a head vortex of the fourth vortex structure to reach or pass the third actuation site. In other words, a third vortex structure is introduced into the first or second local velocity field at a location downstream of the second actuation site, e.g. by ejecting control fluid, and a fourth vortex structure is generated at the first actuation site and allowed to travel into the local high velocity field of the third vortex structure. Thereby, the fourth vortex structure is stabilized and able to travel downstream over a long distance helping to prevent flow separation.
According to a further embodiment, the method comprises capturing a free stream velocity of the fluid flow upstream of the first actuation site, and controlling a delay of activating the second actuator, e.g. to eject control fluid at the second actuation site, and optionally also a delay of activating the third actuator, e.g. to eject control fluid at the third actuation site, based on the captured free stream velocity. A delay, that is, a point of time when control fluid is ejected at the second and, optionally, the third actuation site may be determined based on a captured free stream velocity of the fluid flow. Optionally, also a first, second, or third time period or predefined period of time during which control fluid is ejected at the first, second, or third actuation site may be controlled based on the captured free stream velocity. The delays and the periods of time are also dependent on a spacing of the actuation sites along the direction of flow.
According to another embodiment of the method, a delay activating the second actuator, e.g. to eject control fluid at the second actuation site, and optionally also a delay of activating the third actuator, e.g. to eject control fluid at the third actuation site, is controlled according to a predefined schedule. That is, fixed activation timing may be provided for the actuators. This allows for a very easy and fail safe control of the actuators.
According to an embodiment of the flow body system, the first actuation sites may be formed by openings formed in the flow surface, wherein the first flow control actuators are coupled to the first openings and configured to eject control fluid through the first openings for generating the first vortex structures and the corresponding first local velocity fields, and wherein the second actuation sites are formed by second openings formed in the flow surface, wherein the second flow control actuators are coupled to the second openings and configured to eject control fluid through the second openings for generating the second vortex structures and the corresponding second local velocity fields. In other words, the flow body comprises a row of first openings formed in the flow surface and a row of second openings positioned spaced to the first openings in the second direction. The first flow control actuators are fluid conductively coupled to the first openings and the second flow control actuators are fluid conductively coupled to the second openings. The first and second actuators are configured to eject control fluid, e.g. pressurized air, through the first and second openings, respectively. For example, the first and second actuators may comprise corresponding control structures such as valves, flaps, membranes, nozzles, diffusors, or similar to allow pulsed or continuous ejection of fluid.
According to another embodiment, the first actuators and the second actuators may be realized as plasma actuators. The first and second actuators, for example, each may comprise an electrode arrangement positioned at a respective actuation site on the flow surface, wherein the electrode arrangements are connected to an electric voltage source and configured to generate plasma between a pair of asymmetric electrodes of the respective electrode arrangement.
According to a further embodiment of the flow body system, the flow body may comprise a group of third flow control actuators being coupled to the flow surface at a row of third actuation sites and being configured to generate third vortex structures and corresponding third local velocity fields, the third actuation sites being spaced to one another in the first direction and being positioned spaced to the row of second actuation sites in the second direction, and wherein the controller is communicatively connected to the group of third flow control actuators. Hence, the flow body may comprise at least three rows of actuation sites spaced in the second direction and coupled to respective individually controlled flow control actuators. As explained in detail above in connection with the method of the first aspect, thereby, series of consecutive, highly-energized vortices can be efficiently generated which helps to further prevent flow separation.
According to one embodiment, the third actuation sites are formed by third openings formed in the flow surface, wherein the third actuators are configured to eject control fluid through the third openings for generating the third vortex structures and the corresponding third local velocity fields. Hence, the flow body may comprise a row of third openings formed in the flow surface, the third openings being spaced to one another in the first direction and being positioned spaced to the row of second openings in the second direction, and a group of third flow control actuators coupled to the third openings and configured to eject a control fluid through the third openings, wherein the controller is communicatively connected to the group of third flow control actuators. That is, the flow body may comprise at least three rows of openings, each opening forming an actuation or ejection site for ejecting control fluid by aid of a flow control actuator coupled or connected to the respective opening, the rows being positioned spaced and may extend substantially parallel to each other.
Alternatively, the third actuators may also be realized as plasma actuators as described above for the first and second actuators.
As explained above in connection with the method, the controller may be configured to control the third actuators to eject control fluid or to generate plasma for introducing a third vortex structure into the first local velocity field, when the head vortex of the first vortex structure has propagated with the fluid flow downstream the row of third actuation sites.
Further, the controller may be configured to control the optional third actuators to eject control fluid or to generate plasma for introducing a third vortex structure into a second local velocity field generated by introducing the second vortex structure, when a head vortex of the second vortex structure has propagated with the fluid flow downstream the row of third actuation sites.
Moreover, the controller may also be configured to control the first actuators to eject control fluid or to generate plasma for introducing a fourth vortex structure into the fluid flow, and to control the optional third actuators to continuously eject control fluid or to continuously generate plasma until a head vortex of the fourth vortex structure has propagated downstream the row of third openings.
According to a further embodiment, the flow body system may comprise a sensor device configured to capture a free stream velocity of the fluid flow, the sensor device being arranged upstream of the row of first openings with respect to the second direction, wherein the controller is communicatively connected to the sensor device and configured to control the second actuators and, optionally, the third actuators to be activated, e.g. to eject control fluid or to generate plasma, with a delay based on the captured free stream velocity. The sensor device may comprise one or more velocity sensors, e.g. pitot heads or similar. Optionally, the sensor device may also comprise sensors configured to capture an angle of attack of the fluid flow relative to the second direction.
According to another embodiment the controller may be configured to read a data memory storing a lookup table storing a predefined schedule for activating the first and second actuators. For example, the controller may comprise a data memory storing the lookup table or may read an external data memory. For example, the lookup table may include a series of subsequent time steps, wherein an activation state of each actuator, e.g. “activated” or “deactivated”, is assigned to each time step. The controller, for example, may store software to generate the lookup table based on an input received via an optional input interface, the input including an expected free stream velocity of the fluid flow and a predetermined angle of attack for each time step. In an aircraft, for example, the free stream velocity and the angle of attack may be determined based on a required lift of the aircraft and a predefined curve of climb of the aircraft.
With respect to directions and axes, in particular with respect to directions and axes concerning the extension or expanse of physical structures, within the present disclosure, an extent of an axis, a direction, or a structure “along” another axis, direction, or structure may define that said axes, directions, or structures, in particular tangents which result at a particular site of the respective structures, enclose an angle which is smaller than 45 degrees, preferably smaller than 30 degrees and in particular preferable extend parallel to each other.
With respect to directions and axes, in particular with respect to directions and axes concerning the extension or expanse of physical structures, within the present disclosure, an extent of an axis, a direction, or a structure “crossways”, “across”, “cross”, or “transverse” to another axis, direction, or structure may define that said axes, directions, or structures, in particular tangents which result at a particular site of the respective structures, enclose an angle which is greater or equal than 45 degrees, preferably greater or equal than 60 degrees, and in particular preferable extend perpendicular to each other.
The invention will be explained in greater detail with reference to exemplary embodiments depicted in the drawings as appended.
The accompanying drawings are included to provide a further understanding of the present invention and are incorporated in and constitute a part of this specification. The drawings illustrate the embodiments of the present invention and together with the description serve to explain the principles of the invention. Other embodiments of the present invention and many of the intended advantages of the present invention will be readily appreciated as they become better understood by reference to the following detailed description. The elements of the drawings are not necessarily to scale relative to each other. Like reference numerals designate corresponding similar parts.
In the figures, like reference numerals denote like or functionally like components, unless indicated otherwise. Any directional terminology like “top”, “bottom”, “left”, “right”, “above”, “below”, “horizontal”, “vertical”, “back”, “front”, and similar terms are merely used for explanatory purposes and are not intended to delimit the embodiments to the specific arrangements as shown in the drawings.
Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations may be substituted for the specific embodiments shown and described without departing from the scope of the present invention. Generally, this application is intended to cover any adaptations or variations of the specific embodiments discussed herein.
As is schematically illustrated in
The first openings 11 are formed in the flow surface 1a and may be realized as rectangular slits extending in the first direction L1 as exemplarily shown in
The second openings 12 are formed in the flow surface 1a and may be realized as rectangular slits extending in the first direction L1 as exemplarily shown in
The optional third openings 13 are formed in the flow surface 1a and may be realized as rectangular slits extending in the first, body longitudinal direction L1 as exemplarily shown in
The group of first flow control actuators 21 comprises a number of flow control actuators that may correspond to the number of first openings 11. The first flow control actuators 21 are coupled to the first openings 11 and are configured to eject a control fluid through the first openings 11. Generally, one actuator 21 may be coupled to one or more openings 11. The first flow control actuators 21 may be connected to the first openings 11 via ducts, as schematically shown in
The group of second flow control actuators 22 comprises a number of flow control actuators that may correspond to the number of second openings 12. The second flow control actuators 22 are coupled to the second openings 12 and are configured to eject a control fluid through the second openings 12. Generally, one actuator 22 may be coupled to one or more openings 12. The second flow control actuators 22 may be connected to the second openings 12 via ducts, as schematically shown in
The group of third flow control actuators 23 comprises a number of flow control actuators that may correspond to the number of third openings 13. The third flow control actuators 23 are coupled to the third openings 13 and are configured to eject a control fluid through the third openings 13. Generally, one actuator 23 may be coupled to one or more openings 13. The third flow control actuators 23 may be connected to the third openings 13 via ducts, as schematically shown in
In
The controller 3 is only schematically shown in
As schematically shown in
The optional sensor device 4 may comprise one or more sensors, wherein at least one of those sensors, e.g. a pitot tube, is configured to capture a free stream velocity of a fluid flow S flowing along the flow surface 1. In the example of
As shown in view (A) of
As schematically shown in view (B) of
As shown in views (E) and (F) of
As shown in view (D) of
View (E) of
Moreover, views (E) and (F) of
As shown in
The second head vortex VH2 can be seen in
From a comparison of
By directly comparing
In the foregoing detailed description, various features are grouped together in one or more examples or examples with the purpose of streamlining the disclosure. It is to be understood that the above description is intended to be illustrative, and not restrictive. It is intended to cover all alternatives, modifications and equivalents. Many other examples will be apparent to one skilled in the art upon reviewing the above specification. In particular, the embodiments and configurations described for the seat modules and aircraft infrastructure can be applied accordingly to the aircraft or spacecraft according to the invention and the method according to the invention, and vice versa.
The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. In the appended claims and throughout the specification, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein,” respectively. Furthermore, “a” or “one” does not exclude a plurality in the present case.
While at least one exemplary embodiment of the present invention(s) is disclosed herein, it should be understood that modifications, substitutions and alternatives may be apparent to one of ordinary skill in the art and can be made without departing from the scope of this disclosure. This disclosure is intended to cover any adaptations or variations of the exemplary embodiment(s). In addition, in this disclosure, the terms “comprise” or “comprising” do not exclude other elements or steps, the terms “a” or “one” do not exclude a plural number, and the term “or” means either or both. Furthermore, characteristics or steps which have been described may also be used in combination with other characteristics or steps and in any order unless the disclosure or context suggests otherwise. This disclosure hereby incorporates by reference the complete disclosure of any patent or application from which it claims benefit or priority.
| Number | Date | Country | Kind |
|---|---|---|---|
| 19176248.3 | May 2019 | EP | regional |
