Simplified fluidic oscillator for controlling aerodynamics of an aircraft

Method and apparatus for controlling the aerodynamics of an aircraft using an active flow control system is disclosed herein. In one example, the active flow control system includes an airframe and a plurality of fluidic oscillators. The airframe includes an inlet configured for flight speeds ranging from subsonic to hypersonic. The plurality of fluidic oscillators is mounted about a curvature of the airframe. Each fluidic oscillator includes a body and an integral nozzle coupled to the body. The body has an inflow portion and a narrow nozzle inlet formed opposite the inflow portion. The integral nozzle is coupled to the body by the narrow nozzle inlet. The narrow nozzle inlet forms a single fluid flow path from the inflow portion to the narrow nozzle inlet.

BACKGROUND

The present disclosure relates to fluid flow for an aircraft, and more specifically, to a method and apparatus for controlling the aerodynamics of an aircraft using a fluidic oscillator.

In operating an aircraft, fluid control systems may be used for operation of the aircraft and components within or on the aircraft. The fluid control systems are used during different phases of the operation. For example, the fluid control systems may be used during take-off, in flight, landing, taxiing on the runway, or during other phases of operation while the aircraft is in service. The fluid control systems are used to control the flow of fluid over, in, or through various portions of the aircraft during these phases of operation.

Traditional passive vortex generators, such as vanes and ramps, have demonstrated partial success in controlling separation and improving performance in diffusers. A drawback to the traditional passive vortex generators, however, is that they obstruct the flow path, and therefore, always introduce total pressure loss and increased drag. Additionally, the traditional passive vortex generators are tuned to specific operation conditions, and are not easily made flexible to provide performance improvement across an operating envelope.

Conventional active flow controllers, such as synthetic jets, steady jets, and traditional fluid control actuators, have been shown to be effective at controlling flow separation. These active flow controllers are also capable of being integrated flush with the diffuser so as to not introduce flow obstruction paths. However, the drawback to the conventional active flow controllers is that the performance improvement margins from the passive vortex generators are often not great enough to offset the cost and complexity of installation of the conventional active flow controllers. Thus, the difficulty in installation and high cost of manufacture result in fluid control systems below optimal levels of performance.

SUMMARY

An active flow control system for an aircraft, according to a first example, is disclosed herein. The active flow control system includes an airframe and a plurality of fluidic oscillators mounted about a curvature of the airframe. The airframe has an inlet configured for flight speeds ranging from subsonic to hypersonic. Each fluidic oscillator includes a body and an integral nozzle. The body has an inflow portion and a narrow nozzle inlet formed opposite the inflow portion. The integral nozzle is coupled to the body by the narrow nozzle inlet. The narrow nozzle inlet forms a single fluid flow path from the inflow portion to the narrow nozzle inlet.

The active flow control system for an aircraft according to the first example, wherein the integral nozzle includes curved sidewalls angled with respect to the narrow nozzle inlet.

The active flow control system for an aircraft according to the first example, wherein the angled curved sidewalls create a jet of fluid in a throat of the nozzle.

The active flow control system for an aircraft according to the first example, wherein the formation of the single fluid flow path reduces a size of the fluidic oscillator by at least a factor of 2.

The active flow control system for an aircraft according to the first example, wherein the formation of the single fluid flow path reduces a weight of the fluidic oscillator by at least a factor of 2.

The active flow control system for an aircraft according to the first example, wherein an angle formed between the nozzle and the body of the fluidic oscillator is less than 90 degrees.

The active flow control system for an aircraft according to the first example, wherein the plurality of fluidic oscillators are mounted about a curvature transition of the airframe, upstream of a flow separation.

Moreover, aspects herein include any alternatives, variations, and modifications of the preceding arrangement of configurations of the active flow control system for an aircraft recited above.

An apparatus for managing flow control, according to a second example, is disclosed herein. The apparatus includes a body and an integral nozzle. The body has an inflow portion and a narrow nozzle inlet formed opposite the inflow portion. The integral nozzle is coupled to the body by the narrow nozzle inlet. The narrow nozzle inlet forms a single fluid flow path from the inflow portion to the narrow nozzle inlet.

The apparatus for managing flow control according to the second example, wherein the integral nozzle includes curved sidewalls angled with respect to the narrowed nozzle inlet.

The apparatus for managing flow control according to the second example, wherein the angled curved sidewalls create a jet of fluid in a throat of the nozzle.

The apparatus for managing flow control according to the second example, wherein the formation of the single fluid flow path reduces a size of the fluidic oscillator by at least a factor of 2.

The apparatus for managing flow control according to the second example, wherein the formation of the single fluid flow path reduces a weight of the fluidic oscillator by at least a factor of 2.

The apparatus for managing flow control according to the second example, wherein the narrow nozzle inlet has a first diameter and the integral nozzle has an outlet, formed opposite the narrow nozzle inlet, having a second diameter less than the first diameter.

The apparatus for managing flow control according to the second example, wherein an angle formed between the nozzle and the body of the fluidic oscillator is less than 90 degrees.

Moreover, aspects herein include any alternatives, variations, and modifications of the preceding arrangement of configurations of the apparatus for managing flow control recited above.

A method for managing flow of a fluid, according to a third example, is disclosed herein. The method includes receiving a fluid flow into an inflow portion formed in a body of a fluidic oscillator, transmitting the fluid flow from the inflow portion of the fluidic oscillator to a narrow nozzle inlet formed in the body, opposite the inflow portion, along a single fluid flow path, creating a jet of fluid from the fluid flow in a throat of a nozzle, the nozzle integral with the body at the narrow nozzle inlet, and causing the jet of fluid to exit the nozzle in a direction that changes periodically with time.

The method for managing flow of a fluid according to the third example, wherein the integral nozzle includes curved sidewalls, angled with respect to the narrow nozzle inlet, configured to change the direction of the fluid as the fluid exits the nozzle.

The method for managing flow of a fluid according to the third example, wherein the single fluid flow path reduces a size of each fluidic oscillator by at least a factor of 2.

The method for managing flow of a fluid according to the third example, wherein causing the jet of fluid to exit the nozzle in a direction that changes periodically with time at a low frequency causes the fluid exiting the outlet of the nozzle to sweep across exit of the integral nozzle.

The method for managing flow of a fluid according to the third example, wherein causing the jet of fluid to exit the nozzle in a direction that changes periodically with time at a high frequency causes the fluid exiting the outlet of the integral nozzle to mix jet-energy with a surrounding fluid flow-field.

The method for managing flow of a fluid according to the third example, wherein the single fluid flow path reduces a weight of each fluidic oscillator by at least a factor of 2.

Moreover, aspects herein include any alternatives, variations, and modifications of the preceding arrangement or configurations of the method for managing flow of a fluid recited above.

DETAILED DESCRIPTION

FIG. 1illustrates a conventional fluidic oscillator100for use in an aircraft. The fluidic oscillator100includes a body102and an integral nozzle104coupled to the body102. The body102includes an inflow portion106and a narrow nozzle inlet108formed opposite the inflow portion106. The narrow nozzle inlet108couples the nozzle104to the body102.

A feedback control loop110is formed in the body102of the fluidic oscillator100. The feedback control loop110is configured to create an oscillating jet of fluid that exits the fluidic oscillator100through the nozzle104. The feedback control loop110includes a plurality of feedback channels112,114. When a fluid enters the fluidic oscillator100through the inflow portion106, the fluid is split between the feedback channels112,114, forming two fluid flow paths: a first fluid flow path116through the first feedback channel112and a second fluid flow path118through the second feedback channel114.

The first fluid flow path116and the second fluid flow path118exit the fluidic oscillator100through the nozzle104in an alternating fashion. Assuming that the fluid initially travels along the first side120of the body102, the fluid will follow the first fluid flow path116through the first feedback channel112to the nozzle104. The fluid exits the nozzle104along a second side124of the nozzle104. The fluid exits the nozzle104along the second side124of the nozzle because of the direction of the fluid delivered by the first feedback channel112. Similarly, assuming the fluid initially travels along the second side wall122of the body102, the fluid will follow the second fluid flow path118through the second feedback channel114, and exit the nozzle104along a first side126of the nozzle. The fluid entering the inflow portion106will alternate following the first fluid flow path116and exiting the nozzle104along the second side124of the nozzle104and following the second fluid flow path118and exiting the nozzle104along the first side122of the nozzle104, thus creating an oscillating jet of fluid exiting the nozzle104.

When operating at a high pressure ratio greater than 2.0, the flow physics associated with the high pressure ratio chokes the throat of the fluidic oscillator100, which negates the influence of the feedback control loop110. The jet of fluid relies on the curvature of the nozzle104to exit the fluidic oscillator in an oscillating manner. Thus, at high pressure ratios, the feedback control loop110proves to be unnecessary, and needlessly adds size and weight to the fluidic oscillator100, and results in difficult aircraft integration due to its complicated design.

FIG. 2illustrates an improved fluidic oscillator200for use in an aircraft, according to one example. The fluidic oscillator200includes a body202and an integral nozzle204coupled to the body202. The body202includes an inflow portion206and a narrow nozzle inlet208formed opposite the inflow portion206. The narrow nozzle inlet208couples the nozzle204to the body202. The nozzle204includes curved sidewalls210and an outlet212. The curved sidewalls210are angled with respect to the narrow nozzle inlet208. For example, the curved sidewalls210may be angled between 0° and 90° with respect to the narrow nozzle inlet208. In a specific example, the curved sidewalls210are angled at about 31° with respect to the narrow nozzle inlet208. The outlet212is formed in the nozzle204opposite the narrow nozzle inlet208. The outlet212is sized such that the outlet212has a diameter214larger than a diameter216of the narrow nozzle inlet208. For example, the diameter214of the outlet212may be about 0.04 inches and the diameter216of the narrow nozzle inlet208may be about 0.02 inches. The area enclosed by the narrow nozzle inlet208is referred to as the geometric throat260of the nozzle204.

A single fluid flow path218is formed in the improved fluidic oscillator200from the inflow portion206to the outlet212. As the fluid entering the fluidic oscillator200through the inflow portion206reaches the narrow nozzle inlet208, a jet250of fluid may be formed in the nozzle204. The jet250of fluid is formed provided that the fluid enters the narrow nozzle inlet208at a minimum pressure ratio, such as a pressure ratio greater than 2.0. The minimum pressure ratio chokes the throat260of the fluidic oscillator200, resulting in a Mach number of unity at the throat260. The formation of the jet250in the nozzle204between the sidewalls allows the fluid to exit the nozzle204in an oscillating matter. This is due to the space formed between the jet250and the sidewalls210of the nozzle204. Therefore, the need for a feedback control loop, such as in a traditional fluidic oscillator100, is no longer needed. The removal of the feedback control loop increases vehicle integration potential and reduces fabrication complexity and cost compared to conventional devices and systems. For example, removing the feedback control loop reduces the size and the weight of the traditional fluidic oscillator by at least a factor of 2. These gains are realized without compromising the benefit of the jet exiting the nozzle.

FIG. 3illustrates an aircraft300having an active flow control system301for controlling the aerodynamics of the aircraft300, according to one example. The aircraft300is one example of an aircraft in which the active flow control system301may be implemented as an active flow control system for controlling the aerodynamics of the aircraft. The flow control system may be implemented in the aircraft300to perform various functions, such as maintaining desired airflow. For example, the flow control system301may be used to maintain desired airflow such as a boundary layer over a wing or stabilizer of the aircraft300. In the example shown inFIG. 3, the fluid control system301is implemented to control the flow of fluid beneath a wing of the aircraft300.

The flow control system301includes an airframe302positioned beneath a wing of the aircraft300. In the embodiment shown inFIG. 2, the airframe302is a diffuser. The diffuser302includes an s-shaped elongated body304having a first end306open to ambient air and a second end308. The second end308is an aerodynamic interface plane, where the second end308of the diffuser302meets the compressor of the aircraft300. The diffuser302is coupled to an inlet310at the first end306. An interface311of the diffuser302and the inlet310forms a throat region312. The diffuser302and inlet310are configured for flight speeds ranging from subsonic to hypersonic.

As a fluid enters the inlet310and flows through the diffuser302, the fluid has a tendency to separate from the surface. The flow separation occurs when the fluid becomes detached from the inner surface of the diffuser302, and forms eddies and vortices within the diffuser. The flow separation results in increased drag, such as pressure drag, which is caused by the pressure differential between the front and rear surfaces of the diffuser302as the fluid travels through the diffuser302.

FIG. 4illustrates a cross-sectional view of the diffuser302taken across the A-A line. To control the fluid separation that occurs in the diffuser302, a plurality of fluidic oscillators200are positioned about a curvature of the diffuser302. For example, the fluidic oscillators200may be positioned at the interface311of the diffuser302and the inlet310. Positioning the fluidic oscillators200at the interface311allows the fluidic oscillators200to be positioned upstream of where separation is likely to occur. In another embodiment, the fluidic oscillators200may be positioned downstream of the interface311. The number of fluidic oscillators used may depend on a number of factors, some of which include, the size and weight of each fluidic oscillator, the size of the diffuser302, and the degree of the flow separation. In the example shown inFIG. 4, about fourteen fluidic oscillators are arranged about the curvature transition of the inlet.

FIG. 5illustrates a method500for managing flow of a fluid, according to one example. The method500begins at step502.

At step502, the fluidic oscillator receives a fluid flow into an inlet formed in a body of the fluidic oscillator. The fluidic oscillator may be part of an active flow control system for an aircraft having an airframe with an inlet configured for flight speeds ranging from subsonic to hypersonic. The fluidic oscillators may be mounted about a curvature transition of the inlet. The fluid control system is configured to control the aerodynamics of the aircraft.

At step504, the fluid is transmitted from the inflow portion of the fluidic oscillator to a narrow nozzle inlet formed in the body opposite the inflow portion, along a single fluid flow path. The single fluid flow path is formed by positioning the narrow nozzle inlet opposite the inflow portion of the fluidic oscillator. The fluidic oscillator does not contain a feedback control loop, which is necessary in traditional fluidic oscillators. Thus, there is only a single path the fluid may follow when entering the body of the fluidic oscillator.

At step506, a jet of fluid is created in a throat of a nozzle that is integral with the body of the fluidic oscillator at the narrow nozzle inlet. The nozzle includes curved sidewalls, which, are integral with the narrow nozzle inlet, and an outlet, which is formed opposite the narrow nozzle inlet. The narrow nozzle inlet has a first diameter, which is less than a diameter of the outlet of the nozzle. When the fluid passes through the narrow nozzle inlet, at a minimum pressure ratio, a jet of fluid is created in the throat of the nozzle. The minimum pressure ratio chokes the throat of the fluidic oscillator. For example, a Mach number of unity is sufficient to choke the throat of the fluidic oscillator.

At step508, the jet of fluid is caused to exit the nozzle in a direction that changes periodically with time. The formation of the jet in the throat of the nozzle, between the curved sidewalls, allows the jet of fluid to exit the nozzle in an oscillating matter. This is due to the space formed between the jet and the sidewalls of the nozzle by angling the sidewalls with respect to the narrow nozzle inlet. In one embodiment, the angle between the curved sidewalls and the narrow nozzle inlet is less than 90°. In a specific embodiment, the angle between the curved sidewalls and the narrow nozzle inlet is about 31°. Increasing or decreasing the angle between the curved sidewalls and the narrow nozzle inlet will increase or decrease the frequency at which the jet oscillates upon exit of the nozzle.

When the jet of fluid exits the nozzle, the fluidic oscillator may operate in two specific modes: a sweeping mode and a shedding mode. When the plume in the jet of fluid separates from the nozzle sidewalls, this causes the fluidic oscillator to operate in a sweeping, or low frequency mode (e.g., 10 kHz). As a result, the jet of fluid exiting the nozzle will sweep from side to side with a small angular amplitude (e.g., less than 20° from peak to peak). When the plume begins to break-up, or expand, from the jet of fluid, the fluid oscillator operates in a shedding, or high frequency mode (e.g., 200 kHz). The plume “sheds,” resulting in the spatial and temporal rapid mixing of the jet-energy with the surrounding flow field.

The formation of a single fluid flow path between the inflow portion and the narrow nozzle inlet increases vehicle integration potential and reduces fabrication complexity and cost compared to conventional flow control systems. The simplified fluidic oscillator works as efficiently as the conventional fluidic oscillator at a fraction of the size and weight of the conventional oscillator. Thus, the gains from utilizing a single fluid flow path are realized without compromising the benefit of the jet exiting the nozzle of the fluidic oscillator.