{"id":{"repo_id":"cambridge","oai_identifier":"oai:www.repository.cam.ac.uk:1810/387020"},"canonical_url":"https://search.dev.ndltd.org/etd/cambridge/oai:www.repository.cam.ac.uk:1810/387020","repository":{"repo_id":"cambridge","name":"Cambridge University","base_url":"https://api.repository.cam.ac.uk/server/oai/request"},"display":{"title":"Dissipation in Skewed Boundary Layers","abstract":"The entropy generation within a turbulent, collateral boundary layer is well understood and is characterised by a dissipation coefficient, Cd . However, it is common for the transverse pressure gradients in turbomachines to create highly skewed boundary layers, where the velocity varies in direction as well as magnitude. In this thesis, a combined experimental and high-fidelity computational approach is used to quantify the effect of skew on the dissipation coefficient for the first time. The simulations enable the loss mechanisms responsible for this change in loss to be determined and changes in turbulence structure to be visualised. A new relationship between boundary layer skew and dissipation coefficient is defined and applied to a turbine cascade to demonstrate how surface losses can be better predicted in early-stage design. A turning duct was used to isolate the effects of skew on the boundary layer. At a nominal condition of 14 degrees of skew and Reθ of 1000, the increase in dissipation coefficient is 20% as determined from direct numerical simulation, and 28% from experimental measurements, relative to the collateral boundary layer. Experimental data over a range of skew angles and Reθ values show that Cd increases approximately linearly with skew so that, at a skew of 25°, loss is 70% greater than in the collateral boundary layer. Of the 20% increase in Cd at 14°, 53% is due to increased shear in the mean flow dissipating energy through the action of viscous forces. The addition of a crossflow velocity profile decreases the shape factor of the boundary layer and results in stronger velocity gradients. The other 47% of the increase in dissipation coefficient is due to mean flow energy being converted to turbulent kinetic energy by the action of Reynolds stresses. The arch-like vortex structures responsible for Reynolds stress production are seen to extend further from the wall in the skewed boundary layer than in the collateral case. The implications of the linear increase in Cd with boundary layer skew for loss estimation are examined by evaluating boundary layer loss, in the Harrison turbine cascade, with and without the influence of skew on Cd . By accounting for the skew in the boundary layer, a new proposed model has been used to calculate the loss coefficient in the Harrison Cascade to within 4% of the experimentally measured value. Regions of high losses occurred where both boundary layer edge velocity and skew were high. The newly proposed model guides aerodynamicists by alerting them not only to surfaces with high V 3 but particularly to those with high V 3 and high skew.","abstract_html":"The entropy generation within a turbulent, collateral boundary layer is well understood and is characterised by a dissipation coefficient, Cd . However, it is common for the transverse pressure gradients in turbomachines to create highly skewed boundary layers, where the velocity varies in direction as well as magnitude. In this thesis, a combined experimental and high-fidelity computational approach is used to quantify the effect of skew on the dissipation coefficient for the first time. The simulations enable the loss mechanisms responsible for this change in loss to be determined and changes in turbulence structure to be visualised. A new relationship between boundary layer skew and dissipation coefficient is defined and applied to a turbine cascade to demonstrate how surface losses can be better predicted in early-stage design. A turning duct was used to isolate the effects of skew on the boundary layer. At a nominal condition of 14 degrees of skew and Reθ of 1000, the increase in dissipation coefficient is 20% as determined from direct numerical simulation, and 28% from experimental measurements, relative to the collateral boundary layer. Experimental data over a range of skew angles and Reθ values show that Cd increases approximately linearly with skew so that, at a skew of 25°, loss is 70% greater than in the collateral boundary layer. Of the 20% increase in Cd at 14°, 53% is due to increased shear in the mean flow dissipating energy through the action of viscous forces. The addition of a crossflow velocity profile decreases the shape factor of the boundary layer and results in stronger velocity gradients. The other 47% of the increase in dissipation coefficient is due to mean flow energy being converted to turbulent kinetic energy by the action of Reynolds stresses. The arch-like vortex structures responsible for Reynolds stress production are seen to extend further from the wall in the skewed boundary layer than in the collateral case. The implications of the linear increase in Cd with boundary layer skew for loss estimation are examined by evaluating boundary layer loss, in the Harrison turbine cascade, with and without the influence of skew on Cd . By accounting for the skew in the boundary layer, a new proposed model has been used to calculate the loss coefficient in the Harrison Cascade to within 4% of the experimentally measured value. Regions of high losses occurred where both boundary layer edge velocity and skew were high. The newly proposed model guides aerodynamicists by alerting them not only to surfaces with high V 3 but particularly to those with high V 3 and high skew.","abstract_has_math":false,"creators":["Peacock, Robert"],"institution":"University of Cambridge","degree_name":"Doctor of Philosophy (PhD)","degree_level":"Doctoral","degree_discipline":null,"degree_department":null,"school":null,"contributors":[],"advisors":["Pullan, Graham"],"committee_chairs":[],"committee_members":[],"year":2024,"date_issued":"2024-11-02","date_published":"2024-11-02","updated_at":"2026-07-22T22:23:54Z","subjects":["Boundary layer","Skewed","Aerodynamics","Turbine","Loss","dissipation","turbulence"],"languages":[],"rights":[],"rights_urls":["https://www.repository.cam.ac.uk/bitstreams/9740dd7c-3cfd-4f39-8379-c7369f422c16/download","http://purl.org/NET/rdflicense/allrightsreserved"],"identifier_entries":[]},"links":{"outbound_url":"https://doi.org/10.17863/CAM.119965","outbound_label":"DOI","outbound_source":"dc:identifier.doi"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor.advisor","label":"Advisor","values":["Pullan, Graham"]},{"key":"dc:contributor.sponsor","label":"Sponsor","values":["UK Turbulence Consortium"]},{"key":"dc:creator","label":"Author","values":["Peacock, Robert"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date.issued","label":"Date","values":["2024-11-02"]},{"key":"dc:publisher.institution","label":"Dc Publisher Institution","values":["University of Cambridge"]},{"key":"dc:relation.isreferencedby.uri","label":"Dc Relation Isreferencedby URI","values":["https://www.repository.cam.ac.uk/handle/1810/387020"]},{"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":["Doctor of Philosophy (PhD)"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Boundary layer","Skewed","Aerodynamics","Turbine","Loss","dissipation","turbulence"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:rights","label":"Dc Rights","values":["https://www.repository.cam.ac.uk/bitstreams/9740dd7c-3cfd-4f39-8379-c7369f422c16/download","http://purl.org/NET/rdflicense/allrightsreserved"]},{"key":"dc:rights.embargodate","label":"Dc Rights Embargodate","values":["2026-08-04"]},{"key":"dc:rights.embargotype","label":"Dc Rights Embargotype","values":["embargo"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier.doi","label":"DOI","values":["https://doi.org/10.17863/CAM.119965"]},{"key":"dc:identifier.uri","label":"Identifier URI","values":["https://www.repository.cam.ac.uk/bitstreams/91694023-8c7a-4dec-845e-a92c9c1fe3e8/download"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["The entropy generation within a turbulent, collateral boundary layer is well understood and is characterised by a dissipation coefficient, Cd . However, it is common for the transverse pressure gradients in turbomachines to create highly skewed boundary layers, where the velocity varies in direction as well as magnitude. In this thesis, a combined experimental and high-fidelity computational approach is used to quantify the effect of skew on the dissipation coefficient for the first time. The simulations enable the loss mechanisms responsible for this change in loss to be determined and changes in turbulence structure to be visualised. A new relationship between boundary layer skew and dissipation coefficient is defined and applied to a turbine cascade to demonstrate how surface losses can be better predicted in early-stage design. A turning duct was used to isolate the effects of skew on the boundary layer. At a nominal condition of 14 degrees of skew and Reθ of 1000, the increase in dissipation coefficient is 20% as determined from direct numerical simulation, and 28% from experimental measurements, relative to the collateral boundary layer. Experimental data over a range of skew angles and Reθ values show that Cd increases approximately linearly with skew so that, at a skew of 25°, loss is 70% greater than in the collateral boundary layer. Of the 20% increase in Cd at 14°, 53% is due to increased shear in the mean flow dissipating energy through the action of viscous forces. The addition of a crossflow velocity profile decreases the shape factor of the boundary layer and results in stronger velocity gradients. The other 47% of the increase in dissipation coefficient is due to mean flow energy being converted to turbulent kinetic energy by the action of Reynolds stresses. The arch-like vortex structures responsible for Reynolds stress production are seen to extend further from the wall in the skewed boundary layer than in the collateral case. The implications of the linear increase in Cd with boundary layer skew for loss estimation are examined by evaluating boundary layer loss, in the Harrison turbine cascade, with and without the influence of skew on Cd . By accounting for the skew in the boundary layer, a new proposed model has been used to calculate the loss coefficient in the Harrison Cascade to within 4% of the experimentally measured value. Regions of high losses occurred where both boundary layer edge velocity and skew were high. The newly proposed model guides aerodynamicists by alerting them not only to surfaces with high V 3 but particularly to those with high V 3 and high skew."]},{"key":"dc:format.checksum.md5","label":"Dc Format Checksum Md5","values":["ed952636c98b2eef3bc96a65ef7347d0","87eda9de84448d1f82354d60eee3eb5f"]},{"key":"dc:title","label":"Title","values":["Dissipation in Skewed Boundary Layers"]}]}],"canonical_facts":{"dc:contributor.advisor":["Pullan, Graham"],"dc:contributor.sponsor":["UK Turbulence Consortium"],"dc:creator":["Peacock, Robert"],"dc:date.issued":["2024-11-02"],"dc:description.abstract":["The entropy generation within a turbulent, collateral boundary layer is well understood and is characterised by a dissipation coefficient, Cd . However, it is common for the transverse pressure gradients in turbomachines to create highly skewed boundary layers, where the velocity varies in direction as well as magnitude. In this thesis, a combined experimental and high-fidelity computational approach is used to quantify the effect of skew on the dissipation coefficient for the first time. The simulations enable the loss mechanisms responsible for this change in loss to be determined and changes in turbulence structure to be visualised. A new relationship between boundary layer skew and dissipation coefficient is defined and applied to a turbine cascade to demonstrate how surface losses can be better predicted in early-stage design. A turning duct was used to isolate the effects of skew on the boundary layer. At a nominal condition of 14 degrees of skew and Reθ of 1000, the increase in dissipation coefficient is 20% as determined from direct numerical simulation, and 28% from experimental measurements, relative to the collateral boundary layer. Experimental data over a range of skew angles and Reθ values show that Cd increases approximately linearly with skew so that, at a skew of 25°, loss is 70% greater than in the collateral boundary layer. Of the 20% increase in Cd at 14°, 53% is due to increased shear in the mean flow dissipating energy through the action of viscous forces. The addition of a crossflow velocity profile decreases the shape factor of the boundary layer and results in stronger velocity gradients. The other 47% of the increase in dissipation coefficient is due to mean flow energy being converted to turbulent kinetic energy by the action of Reynolds stresses. The arch-like vortex structures responsible for Reynolds stress production are seen to extend further from the wall in the skewed boundary layer than in the collateral case. The implications of the linear increase in Cd with boundary layer skew for loss estimation are examined by evaluating boundary layer loss, in the Harrison turbine cascade, with and without the influence of skew on Cd . By accounting for the skew in the boundary layer, a new proposed model has been used to calculate the loss coefficient in the Harrison Cascade to within 4% of the experimentally measured value. Regions of high losses occurred where both boundary layer edge velocity and skew were high. 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