{"id":{"repo_id":"vt","oai_identifier":"oai:vtechworks.lib.vt.edu:10919/44416"},"canonical_url":"https://search.dev.ndltd.org/etd/vt/oai:vtechworks.lib.vt.edu:10919/44416","repository":{"repo_id":"vt","name":"Virginia Tech","base_url":"https://vtechworks.lib.vt.edu/oai/request"},"display":{"title":"Analytical investigation of active control of radiated inlet noise from turbofan engines","abstract":"An analytical model has been developed to study the potential of active noise control techniques for reducing radiated tonal inlet noise from turbofan engines. The analytical model consists of multiple control sources placed in the periphery of the engine inlet duct which inject anti-noise into the duct to destructively interfere with the sound field generated by the fan. The development of the analytical expressions of the radiated sound fields due to both the fan disturbance and the control sources is based on duct modal expansion. Numerical analyses are presented for different system configurations of secondary control sources and error sensors. Two error sensing strategies are considered in this work. The first approach uses microphones placed in the acoustic far field. The second sensing technique consists of placing distributed error sensors in the engine inlet. Attenuation of the radiated sound field is accomplished using a multichannel feedforward control approach. Control signals are calculated to minimize the pressure disturbance at desired error sensor locations and are then used to determine the controlled radiated sound field. The performance of selected system configurations are discussed and the sensitivity to system parameter variation to the control of inlet noise is explored. Reductions in the radiated sound power level of 4 to nearly 28 dB is demonstrated. It is also demonstrated that for global attenuation of the far field pressure multiple axial arrays of control sources are required. The model can be used to evaluate performance envelopes for various system configurations including sensitivities to error sensor and control source locations, control channel configurations and the effects of mean flow within the inlet duct. The model can also be extended for use in design optimization.","abstract_html":"An analytical model has been developed to study the potential of active noise control techniques for reducing radiated tonal inlet noise from turbofan engines. The analytical model consists of multiple control sources placed in the periphery of the engine inlet duct which inject anti-noise into the duct to destructively interfere with the sound field generated by the fan. The development of the analytical expressions of the radiated sound fields due to both the fan disturbance and the control sources is based on duct modal expansion. Numerical analyses are presented for different system configurations of secondary control sources and error sensors. Two error sensing strategies are considered in this work. The first approach uses microphones placed in the acoustic far field. The second sensing technique consists of placing distributed error sensors in the engine inlet. Attenuation of the radiated sound field is accomplished using a multichannel feedforward control approach. Control signals are calculated to minimize the pressure disturbance at desired error sensor locations and are then used to determine the controlled radiated sound field. The performance of selected system configurations are discussed and the sensitivity to system parameter variation to the control of inlet noise is explored. Reductions in the radiated sound power level of 4 to nearly 28 dB is demonstrated. It is also demonstrated that for global attenuation of the far field pressure multiple axial arrays of control sources are required. The model can be used to evaluate performance envelopes for various system configurations including sensitivities to error sensor and control source locations, control channel configurations and the effects of mean flow within the inlet duct. The model can also be extended for use in design optimization.","abstract_has_math":false,"creators":["Risi, John D."],"institution":"Virginia Tech","degree_name":"Master of Science","degree_level":"masters","degree_discipline":"Mechanical Engineering","degree_department":"Mechanical Engineering","school":null,"contributors":[],"advisors":[],"committee_chairs":[],"committee_members":[],"year":1995,"date_issued":"1995","date_published":"1995","updated_at":"2026-07-22T22:18:58Z","subjects":[],"languages":["en"],"rights":["In Copyright"],"rights_urls":["http://rightsstatements.org/vocab/InC/1.0/"],"identifier_entries":[{"key":"dc:identifier.other","label":"Dc Identifier Other","values":["etd-08222009-040623"],"render_values":[{"text":"etd-08222009-040623","href":null,"code":true}]}]},"links":{"outbound_url":"http://hdl.handle.net/10919/44416","outbound_label":"Handle","outbound_source":"dc:identifier.uri"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor.department","label":"Department","values":["Mechanical Engineering"]},{"key":"dc:creator","label":"Author","values":["Risi, John D."]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date.accessioned","label":"Dc Date Accessioned","values":["2014-03-14T21:43:37Z"]},{"key":"dc:date.available","label":"Dc Date Available","values":["2014-03-14T21:43:37Z","2009-08-22"]},{"key":"dc:date.issued","label":"Date","values":["1995"]},{"key":"dc:publisher","label":"Institution","values":["Virginia Tech"]},{"key":"dc:type","label":"Dc Type","values":["Thesis"]},{"key":"dc:type.dcmitype","label":"Dc Type Dcmitype","values":["Text"]},{"key":"thesis:degree_discipline","label":"Discipline","values":["Mechanical Engineering"]},{"key":"thesis:degree_level","label":"Degree Level","values":["masters"]},{"key":"thesis:degree_name","label":"Degree Name","values":["Master of Science"]},{"key":"thesis:institution_name","label":"Thesis Institution Name","values":["Virginia Polytechnic Institute and State University"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language.iso","label":"Language (ISO)","values":["en"]},{"key":"dc:rights","label":"Dc Rights","values":["In Copyright"]},{"key":"dc:rights.uri","label":"Rights URI","values":["http://rightsstatements.org/vocab/InC/1.0/"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier.other","label":"Dc Identifier Other","values":["etd-08222009-040623"]},{"key":"dc:identifier.uri","label":"Identifier URI","values":["http://hdl.handle.net/10919/44416"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["An analytical model has been developed to study the potential of active noise control techniques for reducing radiated tonal inlet noise from turbofan engines. The analytical model consists of multiple control sources placed in the periphery of the engine inlet duct which inject anti-noise into the duct to destructively interfere with the sound field generated by the fan. The development of the analytical expressions of the radiated sound fields due to both the fan disturbance and the control sources is based on duct modal expansion. Numerical analyses are presented for different system configurations of secondary control sources and error sensors. Two error sensing strategies are considered in this work. The first approach uses microphones placed in the acoustic far field. The second sensing technique consists of placing distributed error sensors in the engine inlet. Attenuation of the radiated sound field is accomplished using a multichannel feedforward control approach. Control signals are calculated to minimize the pressure disturbance at desired error sensor locations and are then used to determine the controlled radiated sound field. The performance of selected system configurations are discussed and the sensitivity to system parameter variation to the control of inlet noise is explored. Reductions in the radiated sound power level of 4 to nearly 28 dB is demonstrated. It is also demonstrated that for global attenuation of the far field pressure multiple axial arrays of control sources are required. The model can be used to evaluate performance envelopes for various system configurations including sensitivities to error sensor and control source locations, control channel configurations and the effects of mean flow within the inlet duct. The model can also be extended for use in design optimization."]},{"key":"dc:description.degree","label":"Dc Description Degree","values":["Master of Science"]},{"key":"dc:format.medium","label":"Dc Format Medium","values":["BTD"]},{"key":"dc:format.mimetype","label":"Dc Format Mimetype","values":["application/pdf"]},{"key":"dc:title","label":"Title","values":["Analytical investigation of active control of radiated inlet noise from turbofan engines"]}]}],"canonical_facts":{"dc:contributor.department":["Mechanical Engineering"],"dc:creator":["Risi, John D."],"dc:date.accessioned":["2014-03-14T21:43:37Z"],"dc:date.available":["2014-03-14T21:43:37Z","2009-08-22"],"dc:date.issued":["1995"],"dc:description.abstract":["An analytical model has been developed to study the potential of active noise control techniques for reducing radiated tonal inlet noise from turbofan engines. The analytical model consists of multiple control sources placed in the periphery of the engine inlet duct which inject anti-noise into the duct to destructively interfere with the sound field generated by the fan. The development of the analytical expressions of the radiated sound fields due to both the fan disturbance and the control sources is based on duct modal expansion. Numerical analyses are presented for different system configurations of secondary control sources and error sensors. Two error sensing strategies are considered in this work. The first approach uses microphones placed in the acoustic far field. The second sensing technique consists of placing distributed error sensors in the engine inlet. Attenuation of the radiated sound field is accomplished using a multichannel feedforward control approach. Control signals are calculated to minimize the pressure disturbance at desired error sensor locations and are then used to determine the controlled radiated sound field. The performance of selected system configurations are discussed and the sensitivity to system parameter variation to the control of inlet noise is explored. Reductions in the radiated sound power level of 4 to nearly 28 dB is demonstrated. It is also demonstrated that for global attenuation of the far field pressure multiple axial arrays of control sources are required. The model can be used to evaluate performance envelopes for various system configurations including sensitivities to error sensor and control source locations, control channel configurations and the effects of mean flow within the inlet duct. The model can also be extended for use in design optimization."],"dc:description.degree":["Master of Science"],"dc:format.medium":["BTD"],"dc:format.mimetype":["application/pdf"],"dc:identifier.other":["etd-08222009-040623"],"dc:identifier.uri":["http://hdl.handle.net/10919/44416"],"dc:language.iso":["en"],"dc:publisher":["Virginia Tech"],"dc:rights":["In Copyright"],"dc:rights.uri":["http://rightsstatements.org/vocab/InC/1.0/"],"dc:title":["Analytical investigation of active control of radiated inlet noise from turbofan engines"],"dc:type":["Thesis"],"dc:type.dcmitype":["Text"],"thesis:degree_discipline":["Mechanical Engineering"],"thesis:degree_level":["masters"],"thesis:degree_name":["Master of Science"],"thesis:institution_name":["Virginia Polytechnic Institute and State University"]},"updated_at":"2026-07-22T22:18:58Z"}