General Electric Company

Asif A Syed

Robert Eugene Kraft

An acoustic liner is made by placing a raw adhesive septum between a pair of opposite honeycomb cores, and curing the septum to integrally bond the cores thereto.

Acoustic liner manufacture

An acoustic treatment for the air ducts of a gas turbine engine. The acoustic treatment generally includes a facesheet having a plurality of holes therein, a backplate spaced apart from the facesheet, and a plurality of interconnected cells between the facesheet and backplate. Each of the cells is defined by walls attached to the facesheet and the backplate, and at least some of the walls are formed of a porous material so that air is able to flow through the cells in a direction parallel to the facesheet and backplate.

Rigid sandwich panel acoustic treatment

An actively controlled acoustic treatment panel for suppressing noise in a gas turbine engine nacelle including a backsheet formed by a planar matrix of adjacent individually controllable elements, where each of the controllable elements has a transducer and a honeycomb cell enclosing the transducer. A facesheet is also bonded to the controllable elements. A plurality of sensors are positioned within the acoustic treatment panel for sensing acoustic pressure of the noise propagated against the facesheet. A driver is provided for electrically driving each of the transducers to effect displacement thereof in a direction substantially perpendicular to the facesheet. Circuitry is also operatively connected to the pressure sensors and the driver for controlling velocity magnitude and phase of the transducers during displacement, wherein a resulting acoustic impedance at the facesheet achieves a desired acoustic impedance boundary condition at the nacelle. The transducer is further made up of an inner lamination layer, an outer lamination layer, and a piezoelectric membrane positioned between the inner and outer lamination layers, wherein a plurality of aligned openings are provided in the inner and outer lamination layers so that the piezoelectric membrane can be displaced either toward or away from the facesheet.

Actively controlled acoustic treatment panel

The Mach number M.sub.o of flow in the intake nozzle or bypass duct of a gas turbine aircraft engine is determined from the acoustic impedance of a Helmholtz resonator to an engine fan-stator sound source. Pressure measurements P.sub.1 (t) and P.sub.2 (t), made nonintrusively at the duct wall surface and resonator cavity bottom are subjected to Fourier analysis to give P.sub.1 (f) and P.sub.2 (f), and acoustic impedance for the flow is determined from a complex transfer function H.sub.12. Flow Mach number is then established using known acoustic impedance/Mach number correlation relationships or a stored look-up table. An alternative embodiment, utilizes a sound source mounted in the Helmholtz resonator bottom and determines Mach number by pressure measurements made at spaced locations on the resonator chamber wall.

Method and apparatus for nonintrusively determining mach number

A flexible U-shaped channel is abutted against a surface to be measured, thereby forming an acoustic duct, with the surface forming one wall of the duct. An acoustic source injects sound waves into the duct traveling parallel with the surface in order to establish a standing acoustic wave. Measurements of acoustic pressure at several points allows one to compute k.sub.y, the acoustic wave number normal to the surface, and from k.sub.y to compute the acoustic impedance of the surface.

Acoustic impedance measurement

An open-ended acoustic impedance tube is abutted against a material having a known acoustic impedance and a standing wave pattern is established in the tube. A first apparent impedance of the material is derived based on the standing wave pattern. A correction factor is computed based on the known impedance and the first apparent impedance. The open-ended impedance tube is then abutted against a sample material and a second apparent impedance is derived. The actual impedance of the sample is inferred from the second apparent impedance and the correction factor.

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Loveland, OH, United States of America

Asif A Syed