The present invention relates to noise reduction systems for jet engines, and more particularly to a noise reduction system having a plurality of deployable flow-altering components which can be deployed at selected times of operation of a jet engine to thereby reduce the noise generated by the engine.
With ever increasingly stringent noise reduction requirements at airports, noise reduction systems for use with jet engines on private and commercial aircraft are becoming increasingly important. The turbulent mixing of primary-secondary and/or secondary-ambient streams is essentially what produces the broadband jet noise emitted from a jet engine. Takeoff conditions are particularly important since the emitted noise power levels increase with increasing velocity difference between the mixing streams.
Present day noise reduction systems used on commercial aircraft typically involve some form of stationary (i.e., static or fixed geometry) devices, which are often referred to in the industry as “chevrons” or “lobe-mixers”. These fixed devices are typically employed at a downstream edge of an exhaust nozzle and formed so that they protrude into the flow path of the exhaust gas emitted from the jet engine. This causes an intermixing of the exhaust gas with the airstream adjacent the exhaust nozzle. This intermixing serves to reduce the broadband noise generated by the jet engine over a wide range of operating conditions.
The drawback with the above-described, present day chevrons is that such devices, being fixed in their positions, protrude into the exhaust flow at all times during operation of the jet engine. This, of course, generates drag and a loss of thrust. This is important because noise reduction is typically needed only during takeoff of an aircraft and not during cruise conditions. Thus, with present day noise reduction systems that employ fixed chevrons or other like fixed elements, a tradeoff occurs between the needed noise reduction and the desire to avoid the loss of thrust during cruise conditions. As will also be appreciated, noise reduction systems employing fixed chevrons or other like elements which cannot be moved out of the flow path of the exhaust gasses of a jet engine will result in increased fuel burn during cruise operations, thus contributing to increased operating expense for the given aircraft.
It would therefore be highly desirable to provide a noise reducing system for a jet engine used on an aircraft that incorporates a plurality of flow-altering components that can be placed in the flow path of the exhaust flow created by the jet engine during a takeoff condition, but which can be readily retracted out of the flow path once the aircraft reaches a cruise condition. A noise reduction system employing chevrons or other like elements that could be designed to move in a manner that drives disturbances that are closely coupled to the naturally unstable frequencies of the mixing process would be highly desirable in enhancing the initial mixing of the streams without generating large-scale fluid motion. Such a noise reduction system would provide the desired degree of noise reduction during takeoff conditions but would not negatively affect the thrust generated by the engine during cruise conditions, and thus would not negatively impact the amount of fuel required for a given flight.
The present invention is directed to a noise reduction system employing a plurality of deformable flow-altering components that are disposed adjacent a downstream edge of an exhaust nozzle of a nacelle which houses a jet engine. In one preferred form, the flow-altering components comprise a plurality of transduction actuator elements that are deformable (i.e., deployable) in response to the application of an electric current thereto. In a preferred embodiment, an alternating current is applied to the transduction actuators to cause an oscillating motion. The oscillating motion causes the transduction actuators to effectively oscillate into and out of the flow path of the exhaust gas emitted from the jet engine. When no noise reduction is needed, the electric current applied to the transduction actuators is removed and the actuators remain out of the exhaust gas flow path. In this manner, the transduction actuators do not negatively affect the thrust of the engine, and thus do not result in increased fuel burn of the engine. It is anticipated that the transduction actuators will be employed primarily during takeoff conditions and will remain inoperable (i.e., not deployed) during cruise conditions of an aircraft.
In a preferred embodiment the transduction flow-altering components are configured to extend circumferentially around the entire lip portion of the exhaust nozzle. Each of the flow-altering components may comprise a variety of shapes, but in one preferred form they comprise curved surfaces of rectangular platform which project from the lip portion generally parallel to the exhaust gas flow path when the elements are not being excited with an electrical current. Electrically exciting the flow-altering components causes the desired oscillating motion and, consequently, the desired degree of noise reduction needed at a given time during operation of the jet engine. In the preferred embodiments at least one electrical conductor, and more preferably a plurality of such electrical conductors, are provided which extend through bores or channels in the nacelle to the flow-altering components.
Advantageously, the noise reduction system of the present invention does not significantly complicate the construction of the nacelle nor significantly add to the overall cost of an aircraft, nor require significant additional subsystems to be employed on the aircraft.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiments of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.
The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:
The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.
Referring to
Also, while the noise reduction system 10 is shown on the lip portion 12 of the secondary exhaust nozzle 16, it will be appreciated that the system of the present invention could just as readily be employed on the primary exhaust nozzle 20.
With further reference to
With reference to
Referring now to
Disposed between the support ring 38 and notched portion 34 of the lip portion 12 are the flow-altering components 26. As mentioned herein, each flow-altering component 26 is formed by transduction material that bends or deflects in response to an electric current applied thereto. In one preferred form, the transduction material comprises piezoelectric material. It will be appreciated, however, that other types of material such as, for example, magnetostrictive material, could also be employed as the transduction material. Accordingly, it will be understood that while piezoelectric material is especially well suited for use as the transduction material, that the present invention is not limited to the use of only piezoelectric material.
With further reference to
Referring further to
The frequency, phase and amplitude of the signals applied to the flow-altering components 26 may be varied considerably to suit specific applications, since flow instabilities are influenced by each of these factors. In particular, frequency and amplitude set the growth rate of the instability; phase determines the larger scale flow mode or type. The mixing (shear) layers have axial and azimuthal instability modes (and likely others). Different azimuthal modes can be excited by changing the phase of the individual flow-altering components 26 along the circumference of the lip portion 12. For example, if 12 flow-altering components 261–2612 are used, each flow-altering component could be staggered in phase by 30 degrees from its two adjacent flow-altering components. With respect to flow-altering component 261, flow-altering component 262 would be at a phase angle of 30 degrees, flow-altering component 263 would be at a phase angle of 60 degrees, flow-altering component 264 would be at a phase angle of 90 degrees, etc. This arrangement of phase angles would drive the layer in mode 1 or the principal “swirling mode”. If flow-altering components 261–266 were at a phase angle of 0 degrees and flow-altering components 267 to 2612 were at a phase angle of 180 degrees, this would drive a side-to-side motion or a “flapping mode”. If the phase between the flow-altering components 26 is 0 degrees, then only the axisymmetric mode will be driven. This does not mean that this mode is the only one that will exist; one mode can be overcome by another as a fluid element moves downstream. As will be appreciated, there are a plurality of other combinations that could exist. Ideally, one would like to couple to the dominant modes of the flow that the system 10 is trying to influence.
Amplitude is principally important because the frequency and mode of the instability that is excited should be more energetic than other competing instabilities. To alter the growth rate or change the mixing rate of the shear layer, the excitation signal should first be coupled in frequency and phase.
The frequency at which the flow-altering components 26 are caused to oscillate will thus preferably be such that couple with the instability of the initial mixing layer, thus altering the initial turbulence scales, increasing the mixing rate, and reducing the average step velocity. These instabilities can be represented by Strouhal numbers (St) on the order of 0.3, where St equals FD/Uj. The variable “F” represents the frequency, “D” represents the nominal dimension (e.g., jet diameter), and “Uj” is the velocity of the jet. For example, the frequency of the most unstable mode of a 30 inch (76.2 cm) diameter, 1000 ft/second jet would be on the order of 120 Hz. This represents the lower bound of the flow-altering component 26 frequency range. In practice, however, considerably higher driving frequencies may be employed (e.g., 1 to 10 KHz) to effectively couple with the initial mixing layer.
It is a principal advantage of the present invention that when no noise abatement is needed, the flow-altering components 26 can be allowed to return to the position shown in solid lines in
Referring now to
The noise reduction system 10 of the present invention thus provides a means for providing a reduction in the noise emitted from an exhaust nozzle associated with a jet engine without increasing the fuel burn of the jet engine when no noise reduction is needed. The noise reduction 10 effects an oscillating motion of each of the flow-altering components 26 of the system 10 to even more effectively control the intermixing of the exhaust gasses emitted from the exhaust nozzle associated with the jet engine during takeoff conditions of an aircraft, while allowing the flow-altering components 26 to be maintained out of the exhaust gas flow path during cruise conditions so as not to negatively affect the thrust generated by the jet engine.
Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the present invention can be implemented in a variety of forms. Therefore, while this invention has been described in connection with particular examples thereof, the true scope of the invention should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, specification and following claims.
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Number | Date | Country | |
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20030231777 A1 | Dec 2003 | US |