Active control of aircraft engine inlet noise using compact sound sources and distributed error sensors

An active noise control system for reducing aircraft engine noise which emanates from an aircraft engine inlet of a gas turbine engine, said gas turbine engine having a fan and compressor the revolution of which generates a primary sound field, said active noise control system comprising:

• blade passage sensor means mounted within said turbine engine adjacent to said fan for generating a reference acoustic signal;
• distributed error sensor means positioned to be responsive to said primary sound field for generating an error acoustic signal;
• acoustic driver means mounted circumferentially about an interior surface of said inlet preceding said fan;
• and
• controller means responsive to said reference acoustic signal and said error acoustic signal for driving said acoustic driver means to generate a secondary sound field having an approximately equal amplitude but opposite phase as said primary sound field to thereby effectively reduce said engine noise, said acoustic driver means comprises:
• a plurality of curved panels arranged about and conforming to said interior surface, each said curved panel having an interior radius of curvature and an exterior radius of curvature and an exterior surface defined by said exterior radius of curvature;
• and
• surface strain actuator means mounted on said exterior surface of each of said curved panels, said surface strain actuator means being driven by said controller means, said controller means generates a bias voltage to said surface strain actuator means for tuning resonance frequencies of said plurality of curved panels.

A compact acoustic driver for generating a controlled sound field for canceling noise comprising:

• a curved panel tuned to have a fundamental frequency near a tone in said noise to be canceled, and having an interior radius of curvature and an exterior radius of curvature, said curved panel having an exterior surface defined by said exterior radius of curvature;
• surface strain actuator means mounted only on said exterior surface of said curved panel, said surface strain actuator means being mechanically coupled to said curved panel to impart mechanical motion thereto;
• and
• electrical generator means connected to said surface strain actuator means for driving said actuator means and imparting mechanical motion to said curved panel at said fundamental frequency to generate said controlled sound field for canceling said tone in said noise.

A Compact acoustic driver for generating a controlled sound field comprising:

• a curved panel having an interior radius of curvature and an exterior radius of curvature, said curved panel having an exterior surface defined by said exterior radius of curvature;
• surface strain actuator means mounted on said exterior surface of said curved panel, said surface strain actuator means being mechanically coupled to said curved panel to impart mechanical motion thereto;
• and
• electrical generator means connected to said surface strain actuator means for driving said actuator means an imparting mechanical motion to said curved panel to generate said controlled sound field, said electrical generator means drives said actuator means at a frequency approximately equal to a resonance frequency of said curved panel, further comprising means for biasing said actuator means to mechanically stress said curved panel and change the resonance frequency of said curved panel.

For use in an active noise control system for reducing aircraft engine noise which emanates from an aircraft engine inlet of a gas turbine engine, said gas turbine engine having a fan and compressor the revolution of which generates a primary sound field, an array of compact acoustic drivers mounted circumferentially about an interior surface of said inlet preceding said fan for generating a controlled sound field, each said compact acoustic driver comprising:

• a curved panel tuned to have a fundamental frequency near a tone in said aircraft engine noise to be canceled, and having an interior radius of curvature and an exterior radius of curvature, said curved panel having an exterior surface defined by said exterior radius of curvature;
• surface strain actuator means mounted only on said exterior surface of said curved panel, said surface strain actuator means being mechanically coupled to said curved panel to impart mechanical motion thereto;
• and
• electrical generator means connected to said surface strain actuator means for driving said actuator means and imparting mechanical motion to said curved panel at said fundamental frequency to generate said controlled sound field for canceling said tone in said aircraft engine noise.

For use in an active noise control system for reducing aircraft engine noise which emanates from an aircraft engine inlet from a gas turbine engine, said gas turbine engine having a fan and compressor the revolution of which generates a primary sound field, an array of compact acoustic drivers mounted circumferentially about an interior surface of 8aid inlet preceding said fan for generating a controlled sound field, each said compact acoustic driver comprising:

• a curved panel having an interior radius of curvature and an exterior radius of curvature, said curved panel having an exterior surface defined by an exterior radius of curvature;
• surface strain actuator means mounted only on said exterior surface of said curved panel, said surface strain actuator means being mechanically coupled to said curved panel to impart mechanical motion thereto;
• and
• electrical generator means connected to said surface strain actuator means for driving said actuator means and imparting mechanical motion to the curved panel to generate said controller sound field, said electrical generator means drives the actuator means at a frequency approximately equal to a resonance frequency of said curved panel, further comprising means for biasing said actuator means to mechanically stress said curved panel and change the resonance frequency of said curved panel.