REDUCED BLADE VORTEX INTERACTION

A blade includes an elongated body having a leading edge, a trailing edge, a root end, and a tip end, a fluid inlet arranged closer to the root end than the fluid outlet, a fluid outlet arranged near the tip end of the elongated body, and a centrifugal air flow channel defined within the body between the inlet and the outlet to direct air from the inlet to the outlet to issue the flow when the rotor blade is rotating in a rotational path. The blade also includes a valve to selectively open and close the centrifugal air flow channel to selectively issue the flow and change a blade vortex issuing from the rotor blade at discrete portions of the rotational path of the rotor blade. A controller can be operatively connected to the valve to control the valve to open and close the centrifugal air flow channel.

BACKGROUND

The present disclosure relates to blade noise reduction, more specifically to the reduction of rotor blade vortex interaction noise and vibrations typical of rotorcraft (or other propeller aircraft).

2. Description of Related Art

Blade vortex interaction (BVI) noise occurs when an aircraft rotor or propeller blade interacts with a preceding blade's shed and/or tip vortex. Under certain flight conditions (e.g. low speed descent) the rapid change in blade aerodynamic loading associated with this interaction results in a loud and impulsive acoustic event that can increase levels of community annoyance and increase the aircrafts aural detectability. In both civil and military operations, it is desirable to reduce BVI related noise. This interaction can also result in increased vibratory loads.

Many passive and active devices have been proposed to reduce the strength of BVI by manipulating the interactional geometry or altering the strength of the interaction. Such methods and systems have generally been considered satisfactory for their intended purpose under controlled situations but are often too complex or unreliable to warrant regular use. There is still a need in the art for improved low BVI noise rotor designs with low system complexity and high reliability. The present disclosure provides a solution for this need.

SUMMARY

In accordance with at least one aspect of this disclosure, a blade includes an elongated body having a leading edge, a trailing edge, a root end, and a tip end, a fluid inlet arranged closer to the root end than the fluid outlet, a fluid outlet arranged near the tip end of the elongated body, and a centrifugal air flow channel defined within the body between the inlet and the outlet to direct air from the inlet to the outlet to issue the flow when the rotor blade is rotating in a rotational path. The blade also includes a valve to selectively open and close the centrifugal air flow channel to selectively issue the flow and change a blade vortex issuing from the rotor blade at discrete portions of the rotational path of the rotor blade. A controller can be operatively connected to the valve to control the valve to open and close the centrifugal air flow channel.

The outlet can be positioned at or near the distal end of the body to inject flow into the vortex formed and released at the tip end of the rotor blade so as to disrupt the formation, strength and/or displacement of the vortex at or near its point of origin. The outlet can be configured to issue flow perpendicular to the direction of flow around the tip end of the elongated body. However, any other suitable angle relative to the flow to affect the vortex as desired is contemplated herein.

The inlet can be positioned and configured to cause air flow through the air flow channel due to rotation of the rotor blade. In certain embodiments, the inlet can be positioned at or near a root end of the elongated body and can be aligned along any edge or surface of the body (e.g. trailing edge, leading edge, proximal edge, upper surface or lower surface).

The blade can be a helicopter main rotor blade or any other suitable rotating, lift generating body exposed to vortex interaction (e.g. a tiltrotor proprotor blade, a helicopter tail rotor blade, a pusher/tractor propeller blade).

In accordance with at least one aspect of this disclosure, a method of controlling a blade vortex issuing from a rotating rotor blade includes injecting a centrifugal air flow into the blade vortex formed on a rotor blade tip to disrupt the blade vortex at a first location in a rotational path of the rotor blade such that the disrupted blade vortex does not interact with another object, and interrupting the injection of the centrifugal air flow to no longer disrupt the blade vortex at a second location in a rotational path of the rotor blade. The method can include allowing the centrifugal air flow through a centrifugal air flow channel defined in a rotorcraft blade and through an outlet defined in the blade tip of the blade to disrupt the vortex. The method can include actuating a valve disposed within the centrifugal air flow channel to selectively control the centrifugal air flow through the rotorcraft blade at a specific blade positions.

Injecting air flow into the vortex can include injecting air flow at predetermined rotor blade positions to control how the tip vortex interacts with at least one of a main rotor blade, a tail rotor blade, or a proprotor blade. For example, the positions can be chosen so as to modify the interaction with an oncoming blade of the same rotor or so as to modify the interaction with a blade of a separate rotor (e.g. main rotor/tail rotor interaction).

In accordance with at least one aspect of this disclosure a rotorcraft includes a rotorcraft blade similar to the blade as described above. The blade vortex is changed to avoid interacting with another object on the rotorcraft. The valve can open to change the blade vortex when each of the rotor blades is on an advancing side of the rotational path to prevent interacting with another of the rotor blades on the advancing side of the rotational path, and can close when on the retreating side of rotational path.

The rotorcraft can include a second rotor system rotationally disposed on the fuselage, wherein a second valve can open to change the blade vortex when each of the rotor blade is on an advancing side of the rotational path to prevent interacting with the second rotor system, and the second valve can close when on the retreating side of rotational path. A controller can be disposed in the fuselage which controls each of the valves in the rotor blades to selectively open and close the centrifugal air flow channel at the discrete portions of the rotational path of the rotor blade.

DETAILED DESCRIPTION

Reference will now be made to the drawings wherein like reference numerals identify similar structural features or aspects of the subject disclosure. For purposes of explanation and illustration, and not limitation, an illustrative view of an embodiment of a rotor blade in accordance with the disclosure is shown inFIG. 1Aand is designated generally by reference character100. Other embodiments and/or aspects of this disclosure are shown inFIGS. 1B-4. The systems and methods described herein can be used to reduce the acoustic effects of rotor blade tip vortices (e.g., noise due to blade vortex interaction).

Referring toFIGS. 1A-1D, a rotor blade100includes an elongated body101configured to rotate about a hub102and having a leading edge103, a trailing edge104, a root end105and a tip end106. The rotor blade100also includes a centrifugal air flow channel107defined in the body101. The centrifugal air flow channel107includes an inlet108and outlet109. The outlet109is positioned at or near the tip of the body101at near the vortex roll-up formation location such that air flow is injected into the vortex to disrupt the vortex.

As shown inFIG. 1A-1D, the inlet108can be positioned and configured on the rotor blade100such that flow can freely enter into inlet108and travel to outlet109due to rotation of rotor blade100about hub102(e.g., such as a rotorcraft/helicopter blade or propeller). For example, the inlet can be positioned in the trailing edge (e.g.,FIG. 1A), in the leading edge (e.g.,FIG. 1B), in the root end (e.g.,FIG. 1C), in through a partial thickness or entire thickens of the blade (e.g.,FIG. 1D), or in any other suitable location or manner. While the drawings show embodiments with a single inlet, more than one inlet108is contemplated herein on a single blade100. While described as using the rotor blade as a centrifugal pump, it is understood that other types of pumps can be used to pump the air in the channel109, including mechanical pumps and/or vacuums used to create airflow.

Referring toFIG. 2, in certain embodiments, a valve209(e.g., a butterfly valve) can he disposed in the centrifugal air flow channel107to selectively control flow from the inlet108to the outlet109. The valve can be operatively connected to any suitable controller211and/or be configured to mechanically operate in a predetermined manner under predetermined operational regimes (e.g., to open at a certain blade rotational speed, airspeed, blade angle, blade position, or the like). Utilizing a valve209can allow desired control of flow through the centrifugal air flow channel107to issue flow at a desired rate and/or position to control the effect of BVI selectively. For example, allowing flow through the rotor blade100in cruise flight may not be necessary and would lead unnecessary inefficiency such that closing valve209may be preferred. In descent, the valve209can be opened to allow any suitable amount of flow to control BVI as desired (e.g., when landing at slow speeds over populated areas). The controller211can located in the fuselage and/or incorporated into a flight control computer, and be disposed on the rotor hub, or located on a blade100and can communicate using wired and/or wireless technologies.

The flow can be controlled to be steady or unsteady as desired. For example, the valve209can be controlled to fluctuate between an open condition and a closed condition to produce unsteady flow. Bursts may be created by closing the valve209and then opening the valve209. It is also contemplated that rotor blade100can be configured to cause unsteady flow by virtue of its design (e.g., location of the inlet, shape of the rotor blade, other suitable features) which causes pressure fluctuations (e.g., at certain airspeeds).

In certain embodiments, it is contemplated that the valve209can be controlled as a function of its cyclical location (e.g., to be in one or more open states when the blade is advancing and/or to close when retreating). Referring additionally toFIG. 3, a helicopter300is shown issuing flow from the rotor blade100only on the advancing side of a helicopter so as to modify the tip vortex at the position301where it will most likely to encounter an oncoming blade at a later point in time. However, referring toFIG. 4, a helicopter300is shown issuing flow near the tail rotor400so as to modify the main rotor tip vortex at the position where it's trajectory will take it through the tail rotor400. Similarly, referring toFIG. 5, a helicopter300is shown issuing flow near the pusher propeller500so as to modify the main rotor tip vortex at the position where it will pass through the pusher propeller500.

The blade vortex can be changed to avoid interacting with another object on the helicopter300or to alter the strength of the interaction with another object on the helicopter300. As described above, the valve209can open to change the blade vortex when each of the rotor blades is on an advancing side of the rotational path to prevent interacting with another of the rotor blades on the advancing side of the rotational path. The valve209can close when on the retreating side of rotational path.

It is contemplated that the rotorcraft300can include a second rotor system (e.g., a counter rotating rotor, a tail rotor, a pusher prop) rotationally disposed on the fuselage. A second valve209(e.g., disposed in one or more blades of the second rotor system) can open to change the blade vortex when each of the rotor blades is on an advancing side of the rotational path to prevent interacting with the second rotor system. The second valve can close when on the retreating side of rotational path. A controller211can be disposed in the fuselage which controls each of the valves209in the rotor blades to selectively open and close the centrifugal air flow channel at the discrete portions of the rotational path of the rotor blade.

The outlet109can issue flow perpendicular to the direction of flow around the rotor blade. However, any other suitable angle relative to the flow to affect the vortex as desired is contemplated herein. For example, the outlet109can be positioned and/or angled to inject flow into the center of the vortex. While the drawings show embodiments with a single outlet, more than one outlet109is contemplated herein on a single blade100. Also, it is contemplated that the outlet109can be positioned on any suitable portion of the tip.

As disclosed herein, the rotor blade100can be a helicopter main rotor blade or any other suitable rotating, lift generating body exposed to vortex interaction. For example, the rotor blade100can be a tiltrotor proprotor blade, a helicopter tail rotor blade, a pusher/tractor propeller blade, or the like.

In accordance with at least one aspect of this disclosure, a method of controlling a blade vortex issuing from a rotating rotor blade100includes injecting a centrifugal air flow into the blade vortex formed on a rotor blade tip106to disrupt the blade vortex at a first location in a rotational path of the rotor blade100such that the disrupted blade vortex does not interact with another object or interacts at a lower strength. The method also includes interrupting the injection of the centrifugal air flow to no longer disrupt the blade vortex at a second location in a rotational path of the rotor blade100.

The method can include allowing the centrifugal air flow through a centrifugal air flow channel107defined in the rotorcraft blade100and through an outlet109defined in the blade tip106of the blade100to disrupt the vortex. The method can include actuating a valve209disposed within the centrifugal air flow channel107to selectively control the centrifugal air flow through the rotorcraft blade100at a specific blade positions.

Embodiments of this disclosure allow for the reduction of blade vortex interaction (BVI) using centrifugally generated air flow (e.g., via rotation of rotorcraft blades) released at the tip of the rotor blade. Blade tip vortex interaction strength is reduced by means of tip air blowing generated by rotational pumping. Reduced vortex interaction strength reduces BVI noise. Also, air can be released at the blade position corresponding to the release point of the rotor tip vortices that interact with the following blades. The air ejected into the flow produces a change in the vortex core strength, rate of diffusion, and/or vortex position relative to the oncoming blade, either from the same rotor or of another nearby rotor system. This effect is dependent on the strength of the tip vortex (flight condition) and ejected mass flow and rate of change.

While shown as a conventional helicopter, it is understood that aspects of the invention can be used in coaxial helicopters, tilt rotor aircraft, fixed wing aircraft, wind turbine blades, and other situations where blades encounter a vortex interaction.

The methods and systems of the present disclosure, as described above and shown in the drawings provide for rotor blades with superior properties including reduced blade vortex interaction noise and vibration. While the apparatus and methods of the subject disclosure have been shown and described with reference to embodiments, those skilled in the art will readily appreciate that changes and/or modifications may be made thereto without departing from the spirit and scope of the subject disclosure.