The invention is related to methods and apparatuses for controlling fluid flow over surfaces, e.g. air over airfoils, Particularly, the invention is related to methods and apparatuses for controlling vortex generators in order to improve effects of the fluid flow on the surface (e.g. lift and drag) by altering vortex patterns within fluid flow moving across a surface.
Passive vortex generators have been used to optimize air flow in a variety of applications. From sports cars, wind turbines and heat exchangers, to the most commonly known application on wings and other surfaces of aircraft, vortex generators are devices with a wide range of uses. With their simple mechanical design, passive vortex generators are a robust, reliable and inexpensive way of preventing flow separation, to increase lift and decrease drag and/or to improve mixing. This design however also has drawbacks. Being a passive device, such vortex generators cannot be moved or retracted during operation. Thus, it is not possible for such devices to react to different external conditions, like another phase of flight, a different flow velocity or angle of attack.
Vortex generators have been used in a passive manner to prevent or delay flow separation on airfoils and even recent developments of the aerospace industry rely on artificially created vortices to increase lift and decrease drag.
One example of passive vortex generator applications is the placement of strakes on an engine nacelle. Especially in a high-lift configuration and at high angles of attack, the wing area affected by the wake of the engine nacelle and the complex flow field caused by the slat cutout is prone to separation and an associated loss of lift,
Since the nacelle strake is a passive device, it has to be very carefully designed in order to fulfill the requirements regarding the prevention of flow separation at high angles of attack, as well as a preferably low drag penalty caused by the strake itself at low angles of attack, e.g. under a cruise condition. In this case, flow over the wing surface is not prone to influence by the engine mount structure or the nacelle, Therefore, the design of a passive nacelle strake must be a compromise between the optimization for both conditions.
In view of the foregoing, there is a need in the art for methods and apparatuses to control fluid flow over surfaces, such as airflow over wing surface. There is a need for such methods and apparatuses to actively control the generation of vortices to aid reducing skin friction by re-laminarizing the turbulent boundary layer. There is also a need for such methods and apparatuses to operate with fewer moving parts. There is further a need for such systems and methods to be both versatile and cost effective. There is still further a need for such fluid flow control techniques to be applied with water for water vehicles. These and other needs are met by the present invention as described in detail hereafter.
Apparatuses and methods for controlling fluid flow over surfaces, e.g. wings, are disclosed. A system can include a surface influenced by a fluid flow moving across the surface, a vortex generator disposed proximate to the surface, the vortex generator for altering a vortex pattern within the fluid flow moving across the surface, and a controller for activating the vortex generator to alter the vortex pattern within the fluid flow moving across the surface. The vortex generator can comprise one or more fluid injectors each for injecting a fluid jet into the fluid flow driven by gas pressure. The fluid injectors can be disposed along a leading edge of a strake where the strake is disposed on an engine nacelle and the surface comprises an aircraft wing surface. Activation can occur under open or closed loop control with sensors.
One exemplary embodiment of the invention comprises a system for controlling fluid flow including a surface for being influenced by a fluid flow moving across the surface, a vortex generator comprising a strake disposed forward in the fluid flow from the surface, the vortex generator for altering a vortex pattern within the fluid flow moving across the surface by exerting a force at a leading edge of the strake when activated, and a controller for activating the vortex generator to alter the vortex pattern within the fluid flow moving across the surface. Typically, the system can alter the vortex pattern by repositioning the fluid flow and the vortex to re-laminarize a turbulent boundary layer passing the surface. Some embodiments of the invention can further comprise a sensor for sensing an undesirable vortex pattern and triggering the controller to activate the vortex generator. In some embodiments of the invention, the strake can be disposed on an engine nacelle and the surface comprises a wing surface. The surface can be on an aerial or land vehicle where the fluid flow comprises air or on an underwater vehicle where the fluid flow comprises water.
In some embodiments of the invention, the force can be generated by a plasma actuator generating a plasma within the fluid flow. The plasma actuator can comprise a dielectric barrier discharge (DBD) plasma actuator or a corona discharge plasma actuator.
In some embodiments of the invention the vortex generator can comprise one or more actuated vanes disposed along the leading edge of the strake each positionable at a varied pitch against the fluid flow to exert the force. In other embodiments of the invention, the vortex generator can comprise one or more fluid injectors disposed along the leading edge of the strake each for injecting a fluid jet into the fluid flow to exert the force.
For embodiments of the invention where the vortex generator comprises one or more fluid injectors, each fluid jet of the one or more fluid injectors can be driven by gas pressure, e.g. air. At least one fluid jet of the one or more fluid injectors can be injected from a cylindrical port or a rectangular port. The one or more fluid injectors can each be operated independently by the controller to improve different undesirable vortex patterns within the fluid flow.
In some embodiments of the invention, one or more sensors can be used for sensing the vortex pattern within the fluid flow as undesirable and triggering the controller to activate the vortex generator to improve the vortex pattern within the fluid flow, wherein the surface comprises at least a portion of a wing or fuselage surface and the strake is disposed thereon. The one or more sensors can comprise one or more heat flux sensors embedded in the wing or fuselage surface for sensing the vortex pattern as undesirable within the fluid flow. The one or more sensors can comprise one or more pressure sensors embedded in the wing or fuselage surface for sensing the vortex pattern as undesirable within the fluid flow.
Another exemplary embodiment comprises a method for controlling fluid flow including creating a surface for being influenced by a fluid flow moving across the surface, disposing a vortex generator comprising a strake forward in the fluid flow from the surface, the vortex generator for altering a vortex pattern within the fluid flow moving across the surface by exerting a force at a leading edge of the strake when activated, and activating the vortex generator with a controller to alter the vortex pattern within the fluid flow moving across the surface. The method can be further modified consistent with any of the apparatus or system embodiments described herein.
Yet another exemplary embodiment comprises apparatus for controlling fluid flow having a surface for being influenced by a fluid flow moving across the surface, a vortex generator comprising a strake disposed forward from the surface in the fluid flow and comprising one or more fluid injectors disposed on a leading edge of the strake each for injecting a fluid jet into the fluid flow driven by air pressure, the vortex generator for altering a vortex pattern within the fluid flow moving across the surface by exerting a force at the leading edge of the strake and a controller for activating the vortex generator to alter the vortex pattern within the fluid flow moving across the surface. The apparatus can be further modified consistent with any of the method or system embodiments described herein.
In the following description including the preferred embodiment, reference is made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration a specific embodiment in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the present invention.
If the generation of the strake vortex could be actively controlled in a way that enables precise positioning of the vortex, so that the vortex downwash, which transports highly energetic fluid close to the wing's surface, can be positioned exactly where it is needed, a vortex generator can be implemented in a less intrusive manner reducing its size. This can reduce parasitic drag that is induced by the strake.
An optimized and actively controllable vortex position can achieve higher lift, not only at maximum angle of attack, but also over a range of angles of attack. Accordingly, higher wing effectiveness can allow for a smaller wing, reducing aircraft weight while reducing power consumption or improving fuel efficiency and thereby lowering CO2 emissions. In addition to an application on engine nacelle strakes, active vortex control in accordance with the invention can also be implemented in a system to aid reducing skin friction by re-laminarizing the turbulent boundary layer. This can be achieved in applications where the vortex can be sustained stationary close to a surface. Total aircraft drag can be reduced, potentially by as much as a factor of two, which can lead to the aforementioned reductions in fuel consumption, CO2 emissions, electrical power consumption on electrical aircraft, as well as reduced aircraft noise.
An exemplary vortex generator (VG) employing a plurality of gas nozzles mounted on a flat plate (i.e. a wall) or surface can demonstrate that the vortex trajectory can be moved to a wide range of positions by changing the activated nozzle location and thrust. Counter-intuitively, it can be demonstrated that the vortex can be moved closer to the flat plate by a gas nozzle thrusting away from the surface. Similarly, the vortex strength can be increased or decreased by the use of gas nozzles or other types of actuators. Therefore, the vortices can be controlled in position (localization) and intensity over a desired surface, device, or vehicle.
A way to actively influence the position of a vortex, produced by a vortex generator, for example a trapezoidal one, is described hereafter. Wind tunnel data can show that the trajectory of a vortex downstream of the vortex generator can be significantly altered by generating a force along the swept leading edge of the vortex generator. This force can be generated by a plasma jet, air injection through a nozzle, or a positionable element on the vortex generator that deflects the oncoming fluid flow.
Unless an alternate context is provided, “surface” employed in the present application indicates the surface area of interest downstream from and affected by the fluid flow under influence of the vortex generator when activated. Typically, this surface area of interest can be on a separate element from the location of the vortex generator or on a portion of the same element that also supports the vortex generator.
It should also be noted that, although the primary embodiments of the invention described herein refer to air flow and aircraft, the described principles and embodiments can be directly applied to any fluid flow type that can generate vortices affecting a surface it passes. For example, embodiments of the invention can also be applied to incompressible fluid flows such as water as will be understood by those skilled in the art.
One of the most common applications of passive flow control is the usage of vortex generators. Small-aspect-ratio airfoils or tabs attached to a surface over which flow is susceptible to separation produce vortices to move high-energy flow from the outer region of the boundary layer to the wall. The addition of momentum to this area enables the flow to overcome a pressure gradient by mixing with and replacing near-wall flow.
For many years, vortex generators have been used in an extensive variety of applications and are still being taken advantage of, even in the most recent developments, not only in the aerospace sector. Probably the most obvious application is the placement of vortex generators on the upper side of an aircraft's main wing, however they can also be used to increase control surface effectivity, increase pressure recovery over a diffuser or even reduce aerodynamic drag for athletes.
While drag is dramatically reduced by vortex generators when keeping a flow attached that would otherwise be separated, they will increase air resistance at low angles of attack, for example on a wing in cruise flight. When designing an array of vortex generators, multiple parameters have to be taken into consideration to reduce this negative effect as far as possible while still preventing separation under the anticipated flow conditions.
Conventional vortex generators with a height hVG (vortex generator height) of about the boundary layer thickness have been used for many years. Later research has shown that low-profile vortex generators with a height between 10% and 50% could improve performance by lowering the produced drag while still keeping the flow attached. The described later designs however have to be placed more closely to the expected separation point, thereby limiting the operating range.
Wind tunnel tests using plasma actuators (dielectric barrier discharge and corona discharge actuators), and nozzle jets (e.g. air injection) can demonstrate that the trajectory of a vortex downstream from a vortex generator can be significantly altered by generating a force along the swept leading edge of the vortex generator. The force can be delivered to the fluid flow from a plasma jet, an ionic wind actuator, a nozzle jet, a suction slot, or a relatively small vortex generator (e.g. small tab, bump, fin, pin, or any other similar mechanical device) as described hereafter. In one embodiment of the invention, a plurality of smaller vortex generator vanes can be disposed on the leading edge of a larger vortex generator. These devices and/or actuators can be placed not only on the vortex generator leading edge but also on its trailing edges, and/or on both sides if needed. In a further embodiment of the invention, one or more actuators can be placed on the sides of the vortex generator (e.g. on one side or both sides) to produce the desired level of control.
Another example application of vortex generators is the placement of strakes on an aircraft engine's nacelle. Especially in a high-lift configuration and at high angles of attack, the wing area affected by the wake of the engine nacelle and pylon, and the complex flow field caused by the slat cutout is prone to separation and its associated loss of lift. The development and introduction of ultrahigh-bypass and geared turbofan engines with growing fan diameters has further intensified the influence of the nacelle on the attainable CL,max (maximum lift coefficient). To reduce this effect, the strake on the nacelle generates a new strong vortex that prevents the flow structures induced by the engine nacelle and its interaction with the leading-edge high-lift devices from causing premature flow separation.
Since the nacelle strake is a purely passive device, it has to be very carefully designed in order to fulfill the requirements regarding the prevention of flow separation at high angles of attack, as well as a preferably low drag penalty caused by the strake itself at low angles of attack, e.g. cruise condition. In this case, flow over the wing's surface is not prone to influence by the engine mount structure or the nacelle. Therefore, the design of a passive nacelle strake can always only be a compromise between the optimization for both conditions.
If the generation of the strake vortex could be actively controlled in a way that would enable the precise positioning of the vortex, so that its downwash, which transports highly energetic fluid close to the wing's surface, could be positioned exactly where it is needed, the vortex generator could be designed in a less intrusive manner, for example by reducing its size, which would reduce drag that is induced by the strake. Especially in cruise flight, a smaller nacelle strake would allow for lower fuel consumption, while still maintaining functionality under high-angle-of-attack conditions. By optimizing the vortex position through active control, lift could be increased over a range of angles of attack, permitting a smaller wing, reducing aircraft weight and lowering CO2 emissions.
Some embodiments of the invention employ vortex manipulation through plasma actuation. An experimental setup can be used to locate the vortex position and evaluate the influence on the vortex from a plasma actuator by means of an array of static pressure measurements downstream of the vortex generator.
The results of the pressure measurements can show that the vortex can be reliably located with this method. Further experiments can be conducted by placing a dielectric harder discharge (DBD) actuator downstream of the vortex generator. A vortex generator can be mounted on one side of a plate with a plasma actuator positioned between the vortex generator and an array of static pressure holes on the opposite side of the plate. The induced flow of the actuator can be in the same direction as the vortex rotation at the surface. The pressure measurements can show very small increases of static pressure above the position of the vortex, when the plasma actuator is activated, indicating a possible shift of the vortex position, however, no pressure decrease is detected in the area below the vortex that would have been expected, if a change of the vortex position occurs. Accordingly no certain conclusion regarding the influence of the plasma actuation can be drawn. The plasma actuator can also be placed directly on the vortex generator, instead of the surface downstream of the vortex generator, inducing flow in the development phase of the vortex, where the effect should be greatest. A displacement of the vortex away from the surface caused by a reduction of the lift coefficient of the vortex generator when the plasma actuator is active across the vortex generator is contemplated.
In one example embodiment of the invention, air injection can be used to produce the force on the passing fluid flow based on the general description of the vortex generator 700 of
Depending on the application, one or more such vortex generators 1102A, 1102B can be controlled (i.e. have installed actuators or injectors). The hollow vortex generators 1102A, 1102B can be manufactured using conventional subtracting manufacturing (e.g. drilling, mining, casting, electro-machining), additive manufacturing (e.g. metal, composite, or polymer 3D printing) methods, injection molding, resin transfer, powder methods and/or casting techniques among others. Vortex generators 1102A, 1102B could be alternately employed using plasma actuators or positionable elements as previously described. Electrical actuators (e.g. plasma actuators) can be embedded, bonded, and/or deposited using printed electronic techniques or other additive manufacturing processes.
To visualize the effects of the air injection and to determine the exact position of the vortex, a setup was designed and built that allowed the measurement of velocity fields downstream of the vortex generator. These measurements were performed in a small wind tunnel with the vortex generator mounted on a flat wall. Multiple tests were performed with variation of the injection pressure and position (i.e. ports). The vortex generator was mounted at an angle of attack of 20°, supply pressure to the nozzles was regulated to values between 10 and 40 psi. Other pressures and/or angles of attack are possible.
The results show that injection at one or multiple positions on a vortex generator can move the position of the vortex core, both in vertical and horizontal direction. Especially, noteworthy is the fact that an injection at the position closest to the forward tip of the vortex generator (Position 1) can lead to a vertical displacement of the vortex moving it closer to the wall, counter-intuitively to what would be expected when introducing a force away from the wall (see e.g.
One application for embodiments of the invention is the use on aircraft engine nacelle strakes (vanes or chines), which are essentially large vortex generators. Such strikes are common on existing aircraft, useful to inhibit boundary layer separation during low-speed flight, such as take-off and landing, particularly with flaps deployed. The vortex from a nacelle strake flows over the upper surface of the wing, pumping high-momentum fluid towards the surface to inhibit separation. Using leading edge injection to control the vortex produced by the strake can lead to significantly increased effectiveness of these devices. Thus, the present invention allows the position of the vortex to be controlled for different flight conditions for optimum performance.
As described, a vortex can be displaced (or moved) and its circulation can be changed by pneumatic (air injection), small fins/VGs, and/or plasma actuators among other type of actuators mounted on the leading edge of a chine. These actuators generate a force at the leading edge of the chine, where the flow is most sensitive. As a result, the vortex can inhibit separation over the wing and thereby increase aircraft/wing, maximum lift coefficient (CL,max). In this case, the system can reduce noise footprint during takeoff and landing by increasing CL,max. As a result, the needed runway distance can be reduced. Furthermore, the high-lift system (e.g. flaps and slats) can be simplified, thereby reducing the vehicle/structure weight and the complexity (i.e. using less parts and/or smaller areas).
In a further embodiments of the invention, a system can use one or multiple sensors (e.g. pressure sensors, heat flux sensors, optical sensors) that can determine the present state and position of the vortex, and selectively activate the vortex generator elements, establishing a control loop. Such sensors can be disposed in front of the vortex generator (upstream) and/or behind the vortex generator (downstream). Selective activation of the actuator (e.g. injection of air, plasma, or positionable elements) can then operate to manipulate the position of the vortex very precisely to efficiently achieve the desired effect. It should be noted that additional vortex generators of any type described herein can be positioned with any vortex generator in a series configuration to enhance and/or to amplify the control effect.
In a further example embodiment of the invention, optical sensors can also be mounted in such a way that can observe and/or monitor the region of interest with a given view angle (0° to 180°). Such optical sensors can be mounted on any suitable fuselage window or panel pointing towards an area of the wing or fuselage, e.g. as shown in
As described, a controllable vortex using an embodiment of the invention can be used as part of an active vortex control system over a wing surface to re-laminarize a turbulent boundary layer. This can lower total aircraft drag, potentially by as much as a factor of two. Such lower drag corresponds to yielding advantages of lower fuel consumption, CO2 emissions, lower electrical power consumption, and lower noise.
Employing embodiments of the invention, the use of vortex control can be applied to reduce flow separation at transonic flow speed.
In addition, the ability to move a vortex and/or sheet of vortices close to a wall or away from it employing embodiments of the invention provides a way to control heat fluxes through and/or around the wall or surface. A vortex closer to a wall enhances convective heat transfer by transporting heat through the boundary layer. This application can be important for high speed flows or high temperature flows (T∞) where a substrate surface (e.g. wing, fuselage, motor blade, nose, radome, motor case, nozzle, injector, rocket engine) must be kept at a given temperature Tw (max operational temperature) that is below its melting point. It is clear that the vortex control system embodiments of the present invention can increase durability of such structures and/or improve their performance. Such walls or substrates can be used for internal flows and/or external flows applications.
In further embodiments of the invention, a vortex control system according to the described principles can be used to increase heat fluxes to cool down a hot surface (Tw).
In yet further embodiments of the invention, the use of such vortex control can also be applied to enhance or reduce mixing on fluids single specie or multiple species (e.g. chemical reactions, combustion, evaporation) as will be understood by those skilled in the art.
Those skilled in the art will appreciate that the invention illustrated by the various described embodiments herein has application not only on aerial vehicles (aircraft, rotorcraft, drones, engines) and wind turbine systems but also on power plant engines, chemical reactors, rocket engines, underwater vehicles (e.g. submarines) and other underwater devices and structures (e.g. turbines, dams, doors, etc.) where vortices may be present. More broadly, embodiments of the invention can be used anytime a vortex from a vortex generator needs to be controlled.
The foregoing description, including the preferred embodiments of the invention, has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. The above specification provides a complete description of the apparatus, method and use of the invention.
This application claims the benefit under 35 U.S.C. § 119(e) of the following U.S. provisional patent application, which is incorporated by reference herein: U.S. Provisional Patent Application No. 62/938,698, filed Nov. 21, 2019, and entitled “VORTEX CONTROL ON ENGINE NACELLE STRAKE AND OTHER VORTEX GENERATORS,” by Nino et al. (Attorney Docket No. 48593.01US1).
Filing Document | Filing Date | Country | Kind |
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PCT/US2020/061338 | 11/19/2020 | WO |
Number | Date | Country | |
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62938698 | Nov 2019 | US |