Grumman Aerospace Corporation

Northrop Grumman Systems Corporation

Noe Arcas

Charles A Parente

Frederick M Hutto

Shepard G Kay

Belur N Shivashankara

Ronald F Olsen

William C Van Nostrand

Joseph P Gow

Fredrick M Hutto

An extended reaction acoustic liner for use in jet engine noise mitigation has a substantially non-porous outer layer, a honeycomb core disposed in laminar juxtaposition to the outer layer, and a porous inner layer in laminar juxtaposition to the honeycomb core such that the honeycomb core is sandwiched between the outer layer and the inner layer. The honeycomb core comprises a plurality of cell walls defining a plurality of cells. Some of the cells are in fluid communication with one another via the openings formed in the cell walls. The openings in the cell walls cause viscous acoustic losses, resulting in acoustic energy dissipation and enhanced noise attenuation.

Extended reaction acoustic liner for jet engines and the like

A device for measuring the acoustic absorption properties of materials such as liners for jet engines has a first housing, an acoustic driver configured to provide acoustic energy to the first housing, a second housing attached to the first housing, and an acoustic driver configured to provide acoustic energy to the second housing. Acoustic sensors are used to measure the acoustic energy emitted from the two housings and to measure the absorption of each of the housings.

Apparatus and method for measuring the acoustic properties of acoustic

The present invention is embodied in an aircraft engine noise absorption system having a resonator cavity for absorbing incident noise except for a residue noise signal having a predominant frequency, the system comprising an actuator providing an actuator acoustic signal, a noise sensor for sensing the predominant frequency, and a controller for setting the actuator acoustic signal to the predominant frequency and varying one of a phase and an amplitude of the actuator acoustic signal to decrease the residue noise signal.

Noise absorption system having active acoustic liner

A portable two microphone acoustic impedance data acquisition and analysis system provided in a lightweight, fully portable, battery powered instrument with a dual capability of either on-site or remote-site analysis of measured data on the acoustic impedance of acoustically absorbing duct liners of aircraft jet engines. The fully portable instrument is capable of being operated by relatively unskilled personnel to provide acoustic impedance and non-linearity measurements on acoustic liners at airports and aircraft maintenance facilities. The measured data on the engine duct acoustic liner can be an input directly to the data analysis system at the data acquisition site for on-site analysis, or can be recorded for input to a data analysis system at a later time, or can be recorded and transmitted, such as by a telephone modem, to a data analysis system at a remote-site. The remote-site analysis of data eliminates the requirement for skilled personnel at the aircraft to perform the relatively complex data analysis procedures.

Portable acoustic impedance data acquisition and analysis system

A device for permitting evaluation of the acoustic impedance of liner designs used to attenuate noise in engine aircraft inlet and exhaust ducts, and in particular multiple degree of freedom designs of the type which include a porous facesheet followed by a backing depth followed by successive facesheet/backing depth combinations, includes a plurality of spacers of different thicknesses for varying the backing depths, and a movable plunger with a threaded adjustment mechanism for establishing the final backing depth. Gaskets and seals are installed at various interfaces to eliminate noise leakage paths. Two attachment bolts are used to hold the plunger assembly, face sheets, and spacers together, and an alignment disc positioned on the first facesheet is used to properly align an impedance tube waveguide on facesheet.

Multi-degree linear liner impedance testing device

An acoustic attenuating liner has a non-metallic honeycomb core bonded on a backsheet. A corrosion-insulated perforated sheet is bonded to the honeycomb core by adhesive between the perforated sheet and the core. The mesh is woven to a plurality of different determined weave patterns from material on and affixed to the perforated sheet, whereby the mesh has a plurality of different resistances. The mesh is aligned with the perforated sheet and is bonded to the perforated sheet by additional adhesive between the mesh and the perforated sheet, thereby providing a segmented liner with a plurality of facesheet resistances.

Segmented resistance acoustic attenuating liner

An acoustic liner comprising a sound permeable inside plate forming a first closed annulus, and a sound impermeable outside plate forming a second closed annulus located outside of and extending around the first closed annulus. The inside and outside plates are spaced apart and thus form an annular chamber therebetween; and a core member is secured in this annular chamber, between the inside and outside plates. The core member forms or has the shape of a sine wave form annularly extending around the inside plate, and the core member and the inside plate form a multitude of varying depth sound absorption chambers to attenuate sound waves over a broad band of frequencies.

Acoustic liner

An acoustic liner comprising a sound permeable inside plate forming a first closed annulus, and a sound impermeable outside plate forming a second closed annulus located outside of and extending around the first closed annulus. The inside and outside plates are spaced apart and thus form an annular chamber therebetween; and a core member is secured in this annular chamber, between the inside and outside plates. The core member forms or has the shape of a sine wave form annularly extending around the inside plate, and the core member and the inside plate from a multitude of varying depth sound absorption chambers to attenuate sound waves over a broad band of frequencies.

Apparatus and method for determining the steady state flow resistance of face sheets on fully assembled acoustic duct liners. Resistance is measured by subjecting the liner to a sinusoidal acoustic pressure field at the face sheet surface. The pressure field is applied through a cylindrical waveguide and is measured by a pressure transducer flush mounted on the inside of the waveguide near the liner face. A second pressure measurement, obtained by a similar transducer positioned further from the face, is combined with the first measurement to calculate the acoustic resistance for the excitation frequency. If the excitation frequency coincides with the resonant frequency of the liner configuration, then no significant pressure exists on the back surface of the liner face sheet. For this condition the root mean square (rms) pressure measured at the face sheet is equated to the static pressure drop used to obtain the steady state flow resistance. The rms velocity of the oscillating pressure wave is calculated from the ratio of the rms pressure to resistance. A repetition of the procedure for several magnitudes of dynamic pressure permits the development of a curve which describes the non-linear characteristics of resistance with changes in velocity. This curve may be equated to a similar curve obtained using steady state flow resistance measurements of the liner in its partially assembled state without a backing surface.

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Plainview, NY, United States of America

Noe Arcas