Aeronautics and astronautics – Miscellaneous
Reexamination Certificate
2000-02-09
2001-10-02
Jordan, Charles T. (Department: 3644)
Aeronautics and astronautics
Miscellaneous
C244S130000
Reexamination Certificate
active
06296202
ABSTRACT:
RIGHTS OF THE GOVERNMENT
The invention described herein may be manufactured and used by or for the Government of the United States for all governmental purposes without the payment of any royalty.
BACKGROUND OF THE INVENTION
The present invention relates generally to reducing open cavity acoustic resonance, and more particularly to an apparatus for oscillating an aircraft spoiler to reduce acoustic resonance within an open weapons bay of an aircraft in flight.
As is well known in the art, depending on configuration and application, military aircraft will sometimes carry weapons to be discharged during flight within one or more cavities, commonly known as weapons bays. The weapons bays usually include a pair of doors, which are opened only when release of the weapon stores is anticipated. During the remainder of the aircraft flight, the weapons bay doors are closed, presenting a smooth surface to enhance aerodynamic performance as well as other characteristics, such as stealthiness, for example.
When the weapons bay doors are opened in flight, a thin region called a shear layer is created wherein the airflow abruptly transitions from a low speed flow inside the cavity to a high speed flow outside the cavity. This shear layer is characterized by instability which causes the shear layer to form tight, circular rotating pockets of flow commonly referred to as vortices. These vortices impinge on the rear wall of the cavity causing high levels of resonance and high acoustic levels inside the weapons bay. This acoustic resonance can be strong enough to damage the aircraft or its systems, and, therefore, is quite undesirable.
Attempts have been made in the past to reduce acoustic resonance occurring within an open aircraft weapons bay. For example, U.S. Pat. No. 5,699,981 to McGrath et al. describes a system incorporating a cylindrical member disposed on the surface of the aircraft near the leading edge of the cavity. The cylindrical member is projected into the airflow of aircraft in flight to create vortices to reduce acoustic resonance. Similarly, U.S. Pat. No. 5,340,054 to Smith et al. describes an apparatus for acoustic reduction using a series of perturbation pins placed on the surface of the aircraft for generating vortices to disrupt the shear layer, for the purpose of reducing acoustic resonances within an open cavity. While somewhat effective, these prior art systems are not without the need for improvement. For example, these patents describe systems requiring the attachment of structures onto the surface of the aircraft, increasing drag as well as significantly interrupting the desirable smooth aircraft surface. Moreover, their effectiveness decreases dramatically at aircraft speeds up to and exceeding Mach 1.
A system recently described by Parekh, D. E. et al.,
Innovative Jet Flow Control: Mixing Enhancement Experiments,
AIAA Paper No. 96-0308, American Institute of Aeronautics and Astronautics, AIAA, Aerospace Sciences Meeting, 34th, Reno, Nev., Jan. 15-18, 1996, includes vibrating wedges driven by piezoelectric actuators. This system, while providing the proper high frequency range of operation, is unsuited for application to the weapons bay problem because it is incapable of providing sufficient amplitude.
A need exists therefore for an improved aircraft weapons bay acoustic suppression apparatus. Such an apparatus would provide improved acoustic resonance reduction, enhancing aircraft operation as well as contributing to aircraft longevity.
SUMMARY OF THE INVENTION
It is therefore a primary object of the present invention to provide an aircraft weapons bay acoustic suppression apparatus overcoming the limitations and disadvantages of the prior art.
It is another advantage of the present invention to provide an aircraft weapons bay acoustic suppression apparatus providing acoustic resonance reduction over a wide range of aircraft operating conditions.
It is yet another object of the present invention to provide an aircraft weapons bay acoustic suppression apparatus which can be readily incorporated into existing aircraft structures and systems.
It is still another object of the present invention to provide an aircraft weapons bay acoustic suppression apparatus which can be utilized on a wide variety of aircraft.
These and other objects of the invention will become apparent as the description of the representative embodiments proceeds.
In accordance with the foregoing principles and objects of the invention, an aircraft weapons bay acoustic suppression apparatus is provided to dramatically reduce acoustic resonance within an open weapons bay of an aircraft in flight. The apparatus can be incorporated into a wide variety of aircraft and can be utilized in a wide range of operating conditions.
As is known in the art, opening the weapons bay doors in flight gives rise to the creation of a thin region called a shear layer where the airflow abruptly transitions from a low speed flow inside the cavity to a high speed flow outside the cavity. This shear layer is characterized by instability which causes the shear layer to form tight, circular rotating pockets of fluid flow commonly referred to as vortices. These vortices impinge on the rear wall of the cavity and correspondingly generate an acoustic wave which propagates in the opposite way, upstream. The acoustic wave thus generated interacts with the shear layer to influence the size and spacing of the vortices. If the frequency and phase of the acoustic wave coincides with that of the shear layer instabilities, the vortices generated by this “forced” shear layer can become a whole number (1, 2, 3, etc.) with respect to the cavity, generating high levels of undesirable acoustic resonance. The effects of this can be often be strong enough to damage the aircraft or its systems, and, as can be appreciated, are quite undesirable.
According to an important aspect of the present invention, the aircraft weapons bay acoustic suppression apparatus includes a spoiler plate that is oscillated at a frequency designed to seed the shear layer with frequencies which directly compete with the natural frequency of the shear layer vortices. In this way, the damage arising from natural shear layer vortices can reduced or canceled within the weapons bay.
Advantageously, the oscillatable spoiler plate can be mounted on the existing deployable spoiler mounted within the weapons bay. In this way, the spoiler plate can be automatically deployed into the airstream, avoiding the necessity of providing additional deployment structures.
The spoiler plate is oscillated back and forth by a commercially available electromechanical shaker. This has the advantage of providing ready component availability as well as providing the desirable high frequency, high amplitude operation.
As can be seen, the aircraft weapons bay acoustic suppression apparatus of the present invention advantageously provides for a reduction in acoustic resonances within the open bay. The apparatus of the present invention requires few parts, takes up little space and can be readily incorporated into many different aircraft.
REFERENCES:
patent: H324 (1987-09-01), Rubin
patent: 4323209 (1982-04-01), Thompson
patent: 4858850 (1989-08-01), McNay
patent: 5069397 (1991-12-01), Haslund
patent: 5340054 (1994-08-01), Smith et al.
patent: 5520358 (1996-05-01), Kahn et al.
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patent: 6186445 (2001-02-01), Batcho
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Parekh, D. E. et al., Innovative Jet Flow Control: Mixing Enhancement Experiments, AIAA Paper No. 96-0308, American Institute of Aeronautics and Astronautics, AIAA, Aerospace Sciences Meeting, 34th, Reno, NV, Jan. 15-18, 1996.
McGrath et al., Active Control of Shallow Cavity Acoustic Resonance, AIAA Paper No. 96-1949, American Institute of Aeronautics and Astronautics, AIAA Fluid Dynamics Conference,
Best Christian M.
Jordan Charles T.
Kundert Thomas L.
Lambert Richard A.
Scearce Bobby D.
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