Patent Application
20060022092
The present invention relates generally to manipulation of flow field vortices and more particularly, a system and method for manipulating the shedding, size, and trajectory flow field vortices from aerodynamic surfaces with an active array of micro-jets to reduce downstream buffeting and fatigue.
Flow field vortices generated by fluid flow over aerodynamic surfaces can buffet and fatigue any downstream structure exposed to these vortices. Vortices can be generated at the fore body of an aircraft or other upstream structure, and damage control surfaces, engines, after body/empennage, nacelles, turrets, or other structures integrated into the airframe. Additionally, these vortices can be ingested within engine air intakes or other like air inlets leading to poor performance and/or stalling of the aircraft engines. Stalling the aircraft engine creates a potentially hazardous condition.
Next generation aircraft, such as blended wing body, compound this problem by incorporating gas turbine inlets with serpentine spines within the air frame. Additionally, exotic aperture shapes for the inlet and outlet may cause excessive propulsion performance losses. These losses emanate from strong secondary flow gradients in the near wall boundary of the airflow, which produce coherent large-scale vortices.
These vortices can not only cause damage to downstream components on an aircraft, but can seriously damage downstream aircraft as well. To avoid these hazardous inter-aircraft interactions, aircraft are normally separated in time and space to avoid wake turbulence and the buffeting effects of this turbulence on downstream aircraft. Sufficient separation in time and space for take-off, cruise, approach and landing help to ensure that an encounter with another craft's wake turbulence is unlikely or sufficiently weak to avoid causing harm.
In the past, adverse flow field vortices were avoided by redesigning the aircraft in order to remove components from the path of flow field vortices. Alternatively, the components in the path of the flow field vortices were structurally hardened or replaced more frequently to avoid failures resulting from these stresses. Placing components, such as engines or control surfaces, in non-optimal positions in order to reduce these stresses often results in reduced vehicle performance. Similarly, adding structural weight to support increased stress loads caused by the flow field vortices also results in reduced vehicle performance.
Another solution employs passive vortex generator veins to mitigate the effects of flow field vortices. However, these veins result in increased weight and reduced performance over the aircrafts entire operating envelope. Vortex generators are small wing like sections mounted on an aerodynamic surface exposed to the fluid flow and inclined at an angle to the fluid flow to shed the vortices. The height chosen for the best interaction between the boundary layer and the vortex generator is usually the boundary layer thickness. The principle of boundary layer control by vortex generation relies on induced mixing between the primary fluid flow and the secondary fluid flow. The mixing is promoted by vortices trailing longitudinally near the edge of the boundary layer. Fluid particles with high momentum in the stream direction are swept along helical paths toward the duct surface to mix with and, to some extent replace low momentum boundary layer flow. This is a continuous process that provides a source to counter the natural growth of the boundary layer creating adverse pressure gradients and low energy secondary flow accumulation.
The use of vortex generators to reduce distortion and improve total pressure recovery has been applied routinely. Many investigations have been made in which small-geometry surface configurations effect turbulent flow at the boundary layers. Particular attention has been paid to the provision of so-called riblet surfaces in which an array of small longitudinal rib-like elements known as riblets extend over the turbulent boundary layer region of a surface in the direction of fluid flow over the surface, to reduce momentum transport or drag. Experimental results indicate that net surface drag reductions of up to about 7% can be achieved. However, these structure used to induce vortices are fixed and provide no mechanism to actively manipulate the vortex generation needed to improve a dynamic flow condition.
As computers increasingly leaved fixed locations and are used in direct physical applications, new opportunities are perceived for applying these powerful computational devices to solve real world problems in real time. To exploit these opportunities, systems are needed which can sense and act. Micro-fabricated Electro-Mechanical Systems (MEMS) are perfectly suited to exploit and solve these real world problems.
MEMS offer the integration of micro-machined mechanical devices and microelectronics. Mechanical components in MEMS, like transistors in microelectronics, have dimensions that are measured in microns. These electromechanical devices may include discrete effectors and sensors.
Therefore, a need exists for a system and method to shed these flow field vortices to avoid intra-vehicular and inter-vehicular buffeting and fatigue. Furthermore, a need exists for a solution that does not require increased size and weight, or reduced performance.
The present invention provides a system or method to actively control the size and trajectory flow field vortices with micro-jet arrays that substantially addresses the above-identified needs. More particularly, the present invention provides a system or method for shedding flow field vortices from aerodynamic surfaces with active micro-jet arrays to reduce downstream buffeting and fatigue of components exposed downstream components.
Manipulating the shedding, size and trajectory of flow field vortices from an aerodynamic surface involves placing micro-jet arrays at the aerodynamic surface. The individual micro-jets are oriented generally with the flow direction of the fluid flow. These micro-jet arrays induce secondary flow structures within a boundary layer of the fluid flow. The secondary flow structures manipulate the shedding, size and trajectory of the flow field vortices from the surface. In fact, these secondary flow structures or vortices allow the inception point and trajectory and size of the flow field vortices to be actively influenced. By controlling the inception, size, and trajectory of the flow field vortices, it is possible to reduce buffeting and fatigue of downstream components.
Downstream components may include, but should not be limited to; engine inlets buried within the airframe on next generation aircraft, after body, empennage, missiles, turrets, inlet cowls and wings of an aircraft. By reducing the structural loads imposed on these components, the structure required to manage the stress loads on the components may be reduced as well. When a downstream component is an aircraft engine, potentially hazardous conditions can be avoided by preventing the aircraft engine from stalling due to flow field vortices. Additionally, when the downstream component is a submerged engine or one with a reduced or eliminated pylon, the vortices may manipulate the boundary layer obscured by the engine inlet. Such improvements allow reduced observability, improved control, reduced weight and surface area by reducing the pylon or nacelle.
Although the micro-jet arrays may be located anywhere along the aerodynamic surface, one embodiment locates the micro-jets within a receptive zone along the leading edge of aerodynamic surfaces in order to increase the micro-jet's leverage to influence the inception point and trajectory of the flow field vortices. These micro-jets may employ a continuous flow bled from the primary flow or pulsed flows from micro-jets. MEMS offer the integration of micro-machined mechanical devices and microelectronics. Mechanical components in MEMS, like transistors in microelectronics, have dimensions that are measured in microns. These electro-mechanical devices may include discrete effectors and sensors.
Another embodiment senses the flow conditions over the aerodynamic surface. This information is compared with desired fluid flow conditions to actively and dynamically control the micro-jet arrays in order to achieve a desired fluid flow.
Another implementation provides a method to reduce the effect of flow field vortices generated along the surfaces of an upstream vehicle on a downstream vehicle. This involves placing micro-jet arrays on aerodynamic surfaces of the upstream vehicle. These micro-jet arrays are generally oriented with the mean flow direction of the fluid flow over the upstream vehicle's aerodynamic surfaces. Micro-jet arrays introduce secondary flow structures within the boundary layer of the fluid flow over the upstream vehicle. These secondary flow structures influence the inception point, size, and trajectory of flow field vortices associated with the upstream vehicle. By properly directing flow field vortices laterally outward from the upstream vehicle, the separation in time and space between the vehicles may be reduced. This may help improve traffic problems encountered in congested airways.
Yet another embodiment provides an aerodynamic surface or control surface operable to manipulate flow field vortices over the aerodynamic surface. This aerodynamic surface comprises micro-jet arrays located substantially upstream of fluid flow over the majority of the aerodynamic surface. These micro-jet arrays introduce secondary flows in the near wall boundary layer to influence or manipulate the inception point, size, and trajectory of flow field vortices over the aerodynamic surface. Sensors detect fluid flow characteristics over the aerodynamic surface. A control system operably coupled to the micro-jet arrays and sensors directs the micro-jet arrays to actively introduce the secondary flows in order to achieve a desired fluid flow over the aerodynamic surface. Although the micro-jet arrays may be located anywhere on the surface, the array's leverage may be increased by placement within a receptive zone or leading edge.
For a more complete understanding of the present invention and the advantages thereof, reference is now made to the following description taken in conjunction with the accompanying drawings in which like reference numerals indicate like features and wherein:
Preferred embodiments of the present invention are illustrated in the figures like numerals being used to refer to like and corresponding parts of the various drawings.
The present invention provides a system and method for manipulating aerodynamic or hydrodynamic fluid flow over a surface that substantially eliminates or reduces disadvantages and problems associated with previously developed systems and methods. More specifically, the present invention provides a system and method to prevent or minimize exposure of downstream components to buffeting or fatigue through the use of very-small-scale arrays of jets (micro-jets). This system and method includes the placement of micro jet arrays on surfaces bounding the fluid flow. These very-small-scale effectors manipulate the flow behavior of the fluid flow, influence the inception point, size, and trajectory of flow field vortices within the fluid flow, and reduce flow separation within the primary fluid flow.
One potential implementation applies these micro-jet arrays to a vehicle, such as but not limited to aircraft. In
Every aircraft generates counter-rotating vortices from the trailing edge of wingtips, canards or other aerodynamic structures on the aircraft body. Not only can these flow field vortices adversely impact downstream components within a single aircraft. These flow field vortices pose a potential safety hazard for downstream vehicles or aircraft. This is especially true in areas where dense air traffic and aircraft of different weight classes operate. In order to avoid these hazards to downstream vehicles, upstream and downstream vehicles are separated in time and space.
These secondary flow structures 18 influence the inception point, size, and trajectory of flow field vortices over aerodynamic surface 16. A control system, such as micro-jet controller 86, may be operably coupled to micro-jets 12. This control system is operable to actively direct micro-jets 12 to introduce secondary flows 18 in order to achieve a desired fluid flow 14 over aerodynamic surface 16.
This active control may be further complemented by a sensing system operably coupled to the micro-jet controllers. This sensing system may employ flow sensors 80 located at various locations along aerodynamic surface 16. These flow sensors are operable to detect the characteristics of fluid flow 14 over aerodynamic surface 16. Sensor outputs are provided to flow sensor system 82 and processor 84. Processor 84 compares the detected fluid flow characteristics over aerodynamic surface 16 with a desired fluid flow characteristic. Then processor 84 will actively direct micro-jet controller 86 to introduce secondary flows 18 to achieve a desired fluid flow over aerodynamic surface 16.
Processor 84 and controller 86 may be a single processing device or a plurality of processing devices. Such a processing device may be a microprocessor, micro-controller, digital signal processor, microcomputer, central processing unit, field programmable gate array, programmable logic device, state machine, logic circuitry, analog circuitry, digital circuitry, and/or any device that manipulates signals (analog and/or digital) based on operational instructions.
As previously stated, these micro-jets and flow sensors may be incorporated in any aerodynamic surface. However, in many instances, more value may be realized by placing these systems within receptive zones of the aerodynamic surface such as the leading edge of the aerodynamic surfaces. The desired fluid flow may avoid having flow field vortices adversely impact downstream components. The desired fluid flow also reduces the fatigue or buffeting of downstream components.
The micro-jets are very-small-scale devices. In some embodiments theses jets are on the order of one-tenth of the boundary layer thickness. These micro-jets may be miniature vortex generators or vortex generator jets fabricated in many ways and applied as an appliqué to or cast into the surface. The micro-jets may be miniature fluidic jets that introduce momentum in the form of micro-jet flows 20. These micro-jet flows may be continuous or pulsed and may be bled from the primary flow associated with an engine. Micro-jets may also be micro fabricated mechanical structures incorporated on or in the aerodynamic surface. These may also be synthetic pulsators. Other similarly sized jets, known to those skilled in the art, may also be used as the micro-jets.
Sensor system 82 may receive input from conventional flow sensors or micro fabricated electromechanical sensor devices such as those illustrated in
Another embodiment provides an aerodynamic control surface that actively manipulates the inception point, size and trajectory of flow field vortices and/or boundary layer separation over the aerodynamic control surface. This aerodynamic control surface will have micro-jet arrays located substantially upstream of fluid flow over the control surface. These micro-jet arrays introduce secondary flows in the near wall boundary layer. These secondary flows reduce boundary layer separation over the aerodynamic control surface. By reducing boundary layer separation, the overall size of the control surface as well as support for the control surface may be reduced. In an aircraft, for example, this may result in significant weight reduction as the structural requirements associated with the aircraft control surfaces and their control systems may be reduced. A control system operably coupled to the micro-jet arrays may direct micro-jet arrays to introduce secondary flows in order to achieve desired fluid flow over the control surface.
Another embodiment takes the form of an aircraft such as that depicted in
The present invention enables new and improved designs of low-observable tactical aircraft by allowing unconventionally aerodynamic shapes. Low-observable in part takes into consideration such as detection by radar and the radar cross-section associated with a low-observable aircraft.
One method to detect aircraft involves the use of radar. However, not all objects or aircraft reflect the same amount of radar waves, as is known by those skilled in the art. In a low-observable aircraft one would want to reflect as little radar energy as possible to a radar receiver, enabling the plane to go undetected at closer ranges. The amount of radar energy that is reflected by an object can be defined by its radar cross-section. To define the radar cross-section of a target, one calculates the size of a sphere, which would reflect the same amount of radar energy as the aircraft that was measured. The radar cross-section in the square meters is then the area of a circle of the same diameter as the imaginary sphere.
Radar cross-section is not necessarily defined by aircraft size, but is more closely related to its design and construction. Curved surfaces reflect energy in many directions. Therefore, curved surfaces have been historically avoided in favor of flat surfaces. Flat surfaces, like the facets of a diamond, reflect energy in the limited directions of the designers' choice-namely, away from detecting receivers for a low observable aircraft. As the computation power of computers have increased designers need no longer be limited to faceted surfaces, rather surfaces, including curved surfaces, may be modeled and optimized to minimize the amount of radar energy reflected to a detecting receiver.
One problem source of radar signatures from aircraft has been associated with the engine ducting. In some instances this has been used as an identifier of the aircraft. Modern radars can look down engine inlets to bounce returns off the highly reflective compressor blades (and in many cases identify them by counting the rotating blades). Radar is not the only method of aircraft detection. To reduce their vulnerability to heat-seeking detection systems, low-observable aircraft may use slit-like inlets and exhausts. Exhaust may emerge in cool, diffuse fans rather than hot, concentrated streams.
These devices may be used in a low-observable aircraft surfaces or unconventionally shaped surfaces. In addition to aircraft applications, static architectural structures such as buildings, bridges, and towers may incorporate these devices in their aerodynamic surfaces. Unconventionally shaped surfaces may include aggressive duct offsets. The enhancement of fluid flow 14 over these unconventionally shaped surfaces can help to minimize the size, weight, and structural support required by these surfaces.
Finally, the low-observable requirements for inlet and exhaust ducting pose significant challenges. The challenges require high aspect ratio and exotic aperture shaping of ducts or top-mounted inlets for ducts. Fluid flow control can be used to mitigate any performance impact on the aircraft. Additionally, attack geometries and sensing internal and external flow conditions at the aircraft and actively manipulating the fluid flow conditions at the aircraft to achieve desired fluid flow conditions at the aircraft will enhance dynamic conditions of the aircraft in flight. Fluid flow may be manipulated to meet several objectives including: (1) reduced component fatigue, (2) stable fluid flow within an internal ducting system, and (3) stable fluid flow external to the aircraft in dynamic geometries.
Additionally, flow control can reduce cyclic fatigue of components located within fluid flow 14. Stress peak amplitudes experienced by a component within the fluid flow for a normal flow can be greatly reduced by reducing or eliminating interactions between flow field vortices and structural components.
The present invention may be used to improve flow behavior in a hydrodynamic application. This may minimize head loss in a piping system, reduce flow noise within a piping system or over a submerged structure or to control and manipulate hydrodynamic flow about a watercraft for direction and thrust control.
Further embodiments of the present invention may include air-handling units such as HVAC systems, chemical processors, automobile air intake manifold or biomedical applications. However, the present invention should not be limited to these applications.
As one of average skill in the art will appreciate, the term “substantially” or “approximately”, as may be used herein, provides an industry-accepted tolerance to its corresponding term. Such an industry-accepted tolerance ranges from less than one percent to twenty percent and corresponds to, but is not limited to, component values, integrated circuit process variations, temperature variations, rise and fall times, and/or thermal noise. As one of average skill in the art will further appreciate, the term “operably coupled”, as may be used herein, includes direct coupling and indirect coupling via another component, element, circuit, or module where, for indirect coupling, the intervening component, element, circuit, or module does not modify the information of a signal but may adjust its current level, voltage level, and/or power level. As one of average skill in the art will also appreciate, inferred coupling (i.e., where one element is coupled to another element by inference) includes direct and indirect coupling between two elements in the same manner as “operably coupled”. As one of average skill in the art will further appreciate, the term “compares favorably”, as may be used herein, indicates that a comparison between two or more elements, items, signals, etc., provides a desired relationship. For example, when the desired relationship is that signal 1 has a greater magnitude than signal 2, a favorable comparison may be achieved when the magnitude of signal 1 is greater than that of signal 2 or when the magnitude of signal 2 is less than that of signal 1.
Although the present invention has been described in detail herein with reference to the illustrative embodiments, it should be understood that the description is by way of example only and is not to be construed in a limiting sense. It is to be further understood, therefore, that numerous changes in the details of the embodiments of this invention and additional embodiments of this invention will be apparent to, and may be made by, persons of ordinary skill in the art having reference to this description. It is contemplated that all such changes and additional embodiments are within the spirit and true scope of this invention as claimed below.
