{"id":{"repo_id":"soton","oai_identifier":"oai:eprints.soton.ac.uk:52085"},"canonical_url":"https://search.dev.ndltd.org/etd/soton/oai:eprints.soton.ac.uk:52085","repository":{"repo_id":"soton","name":"University of Southampton","base_url":"https://eprints.soton.ac.uk/cgi/oai2"},"display":{"title":"Prediction and control of sound propagation in turbofan engine bypass ducts","abstract":"This thesis contains original research into the propagation of sound in acoustically lined ducts
with flow. The motivation for this work is the requirement to predict the sound attenuation of
acoustic liners in the bypass duct of modern turbofan aeroengines. The liners provide the most
effective means with which to suppress the rear fan noise. It is therefore important to make
the best possible use of the available lined area by optimising the liner configuration. A set
of analytic and numerical methods for predicting the liner attenuation performance have been
developed, which are suitable for use in intensive liner optimisation studies, or as preliminary
design tools.
Eigenvalue solvers have been developed to find modal solutions in rectangular ducts with
uniform flow and annular ducts with sheared flow. The solvers are validated by replicating
results from the scientific literature and the Finite Element method. The effect of mean core
flow radial profile and boundary layers on the mode eigenfunctions and axial decay rates are
considered. It is shown that solutions for thin boundary layer flows converge to those based on
the commonly used slip flow boundary condition. It is demonstrated that realistic flow profiles
should be used to assess acoustic mode propagation in bypass ducts. The flow profile can have
strong effects upon low order modes and surface waves, and in fact at high frequencies, the
profile can affect all the modes.
Mode-matching schemes are developed to assess the power attenuation performance and
modal scattering of finite length liners. The results of the schemes are used to show that refraction
of sound by boundary layers increases attenuation at high frequency. Power attenuation
is higher where the mean core flow gradient refracts sound towards the liner. It is found that
asymmetric liners can provide improved attenuation, depending on the direction of the mean
flow shear gradient.
The optimisation of axially-segmented liners for single and multi-mode sources is demonstrated.
It is found that potentially large improvements in the attenuation of tonal noise is possible,
whilst benefits for broadband noise are more difficult to achieve.","abstract_html":"This thesis contains original research into the propagation of sound in acoustically lined ducts<br/>with flow. The motivation for this work is the requirement to predict the sound attenuation of<br/>acoustic liners in the bypass duct of modern turbofan aeroengines. The liners provide the most<br/>effective means with which to suppress the rear fan noise. It is therefore important to make<br/>the best possible use of the available lined area by optimising the liner configuration. A set<br/>of analytic and numerical methods for predicting the liner attenuation performance have been<br/>developed, which are suitable for use in intensive liner optimisation studies, or as preliminary<br/>design tools.<br/>Eigenvalue solvers have been developed to find modal solutions in rectangular ducts with<br/>uniform flow and annular ducts with sheared flow. The solvers are validated by replicating<br/>results from the scientific literature and the Finite Element method. The effect of mean core<br/>flow radial profile and boundary layers on the mode eigenfunctions and axial decay rates are<br/>considered. It is shown that solutions for thin boundary layer flows converge to those based on<br/>the commonly used slip flow boundary condition. It is demonstrated that realistic flow profiles<br/>should be used to assess acoustic mode propagation in bypass ducts. The flow profile can have<br/>strong effects upon low order modes and surface waves, and in fact at high frequencies, the<br/>profile can affect all the modes.<br/>Mode-matching schemes are developed to assess the power attenuation performance and<br/>modal scattering of finite length liners. The results of the schemes are used to show that refraction<br/>of sound by boundary layers increases attenuation at high frequency. Power attenuation<br/>is higher where the mean core flow gradient refracts sound towards the liner. It is found that<br/>asymmetric liners can provide improved attenuation, depending on the direction of the mean<br/>flow shear gradient.<br/>The optimisation of axially-segmented liners for single and multi-mode sources is demonstrated.<br/>It is found that potentially large improvements in the attenuation of tonal noise is possible,<br/>whilst benefits for broadband noise are more difficult to achieve.","abstract_has_math":false,"creators":["Brooks, Christopher James"],"institution":"University of Southampton","degree_name":"Ph.D.","degree_level":"doctoral","degree_discipline":null,"degree_department":null,"school":null,"contributors":[],"advisors":["McAlpine, Alan","Kempton, Andrew"],"committee_chairs":[],"committee_members":[],"year":2007,"date_issued":"2007-09","date_published":"2007-09","updated_at":"2026-07-24T04:35:50Z","subjects":[],"languages":[],"rights":[],"rights_urls":[],"identifier_entries":[]},"links":{"outbound_url":null,"outbound_label":null,"outbound_source":null},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor.advisor","label":"Advisor","values":["McAlpine, Alan","Kempton, Andrew"]},{"key":"dc:creator","label":"Author","values":["Brooks, Christopher James"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date","label":"Dc Date","values":["2007-09"]},{"key":"dc:date.issued","label":"Date","values":["2007-09"]},{"key":"dc:publisher.department","label":"Dc Publisher Department","values":["Fluid Dynamics & Acoustics Group (pre 2011 reorg)","Institute of Sound and Vibration Research"]},{"key":"dc:publisher.institution","label":"Dc Publisher Institution","values":["University of Southampton"]},{"key":"dc:relation.isreferencedby","label":"Dc Relation Isreferencedby","values":["https://eprints.soton.ac.uk/52085/"]},{"key":"dc:type","label":"Dc Type","values":["Thesis"]},{"key":"dc:type.qualificationlevel","label":"Dc Type Qualificationlevel","values":["doctoral"]},{"key":"dc:type.qualificationname","label":"Dc Type Qualificationname","values":["Ph.D."]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier.uri","label":"Identifier URI","values":["https://eprints.soton.ac.uk/52085/1/P2478.pdf"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["This thesis contains original research into the propagation of sound in acoustically lined ducts
with flow. The motivation for this work is the requirement to predict the sound attenuation of
acoustic liners in the bypass duct of modern turbofan aeroengines. The liners provide the most
effective means with which to suppress the rear fan noise. It is therefore important to make
the best possible use of the available lined area by optimising the liner configuration. A set
of analytic and numerical methods for predicting the liner attenuation performance have been
developed, which are suitable for use in intensive liner optimisation studies, or as preliminary
design tools.
Eigenvalue solvers have been developed to find modal solutions in rectangular ducts with
uniform flow and annular ducts with sheared flow. The solvers are validated by replicating
results from the scientific literature and the Finite Element method. The effect of mean core
flow radial profile and boundary layers on the mode eigenfunctions and axial decay rates are
considered. It is shown that solutions for thin boundary layer flows converge to those based on
the commonly used slip flow boundary condition. It is demonstrated that realistic flow profiles
should be used to assess acoustic mode propagation in bypass ducts. The flow profile can have
strong effects upon low order modes and surface waves, and in fact at high frequencies, the
profile can affect all the modes.
Mode-matching schemes are developed to assess the power attenuation performance and
modal scattering of finite length liners. The results of the schemes are used to show that refraction
of sound by boundary layers increases attenuation at high frequency. Power attenuation
is higher where the mean core flow gradient refracts sound towards the liner. It is found that
asymmetric liners can provide improved attenuation, depending on the direction of the mean
flow shear gradient.
The optimisation of axially-segmented liners for single and multi-mode sources is demonstrated.
It is found that potentially large improvements in the attenuation of tonal noise is possible,
whilst benefits for broadband noise are more difficult to achieve."]},{"key":"dc:format","label":"Dc Format","values":["text"]},{"key":"dc:title","label":"Title","values":["Prediction and control of sound propagation in turbofan engine bypass ducts"]}]}],"canonical_facts":{"dc:contributor.advisor":["McAlpine, Alan","Kempton, Andrew"],"dc:creator":["Brooks, Christopher James"],"dc:date":["2007-09"],"dc:date.issued":["2007-09"],"dc:description.abstract":["This thesis contains original research into the propagation of sound in acoustically lined ducts
with flow. The motivation for this work is the requirement to predict the sound attenuation of
acoustic liners in the bypass duct of modern turbofan aeroengines. The liners provide the most
effective means with which to suppress the rear fan noise. It is therefore important to make
the best possible use of the available lined area by optimising the liner configuration. A set
of analytic and numerical methods for predicting the liner attenuation performance have been
developed, which are suitable for use in intensive liner optimisation studies, or as preliminary
design tools.
Eigenvalue solvers have been developed to find modal solutions in rectangular ducts with
uniform flow and annular ducts with sheared flow. The solvers are validated by replicating
results from the scientific literature and the Finite Element method. The effect of mean core
flow radial profile and boundary layers on the mode eigenfunctions and axial decay rates are
considered. It is shown that solutions for thin boundary layer flows converge to those based on
the commonly used slip flow boundary condition. It is demonstrated that realistic flow profiles
should be used to assess acoustic mode propagation in bypass ducts. The flow profile can have
strong effects upon low order modes and surface waves, and in fact at high frequencies, the
profile can affect all the modes.
Mode-matching schemes are developed to assess the power attenuation performance and
modal scattering of finite length liners. The results of the schemes are used to show that refraction
of sound by boundary layers increases attenuation at high frequency. Power attenuation
is higher where the mean core flow gradient refracts sound towards the liner. It is found that
asymmetric liners can provide improved attenuation, depending on the direction of the mean
flow shear gradient.
The optimisation of axially-segmented liners for single and multi-mode sources is demonstrated.
It is found that potentially large improvements in the attenuation of tonal noise is possible,
whilst benefits for broadband noise are more difficult to achieve."],"dc:format":["text"],"dc:identifier.uri":["https://eprints.soton.ac.uk/52085/1/P2478.pdf"],"dc:publisher.department":["Fluid Dynamics & Acoustics Group (pre 2011 reorg)","Institute of Sound and Vibration Research"],"dc:publisher.institution":["University of Southampton"],"dc:relation.isreferencedby":["https://eprints.soton.ac.uk/52085/"],"dc:title":["Prediction and control of sound propagation in turbofan engine bypass ducts"],"dc:type":["Thesis"],"dc:type.qualificationlevel":["doctoral"],"dc:type.qualificationname":["Ph.D."]},"updated_at":"2026-07-24T04:35:50Z"}