{"id":{"repo_id":"cambridge","oai_identifier":"oai:www.repository.cam.ac.uk:1810/387100"},"canonical_url":"https://search.dev.ndltd.org/etd/cambridge/oai:www.repository.cam.ac.uk:1810/387100","repository":{"repo_id":"cambridge","name":"Cambridge University","base_url":"https://api.repository.cam.ac.uk/server/oai/request"},"display":{"title":"The effects of pressure waves on turbulent oblique shock wave boundary layer interactions in rectangular channels","abstract":"Oblique Shock Wave--Boundary-Layer interactions (oblique SBLIs) occur in many practical applications, such as in mixed compression supersonic jet intakes and transonic compressor cascades and can have significant detrimental effects on the downstream boundary layer, resulting in flow distortion, increased turbulent fluctuations, and pressure losses. They often occur near to a side-wall, such as in rectangular intakes, which introduces a side-wall boundary layer. At the intersection of the primary surface and the side-wall, a thick corner boundary layer is formed containing low momentum which separates readily at an adverse pressure gradient. The corner boundary layer separates further upstream than the primary separation and displaces the incoming flow. This generates corner compression and expansion waves which propagate into the primary interaction. Previous investigations have examined the effects of corner pressure waves on the interaction with the use of bluff block bodies placed in the streamwise corners of a supersonic wind tunnel which generate large corner separations. These blocks were shifted in the streamwise direction relative to the primary interaction in order to impart a varying corner wave influence. However, the corner compression and expansion waves are generated in relatively close proximity, with the result that the differing effects of these waves on the interaction could not be conclusively established. In this investigation conical corner bodies are used to generate corner compression and expansion waves with a clear physical separation between them. Experiments were run in a supersonic wind tunnel at Mach 2.5, with an incident shock deflection angle of 8°, and a Reynolds number based on the incoming boundary layer thickness of 1.8 x 10^5. The corner cones are placed in a range of streamwise locations to induce a varying corner influence on the interaction. This resulted in highly three-dimensional separation geometries in some cases and a wide range of centreline separation lengths, varying between 0.2 and 2.8 times the baseline case. A quasi-two-dimensional relationship between the local separation length and pressure along streamwise strips through the interaction was established. This is surprising given the strong three-dimensionality of these interactions. This relationship also confirms the qualitative observations of previous investigations that compression waves arriving over the interaction cause the separation length to increase, while expansion waves have the opposite effect. It was also found that corner waves arriving upstream of the interaction had a secondary influence on the separation length, while downstream waves had a greater than expected upstream influence. However, further work is required to explore the effects of up- and downstream waves on the interaction. Surface bumps were considered as an alternative method of introducing pressure waves into the interaction, and as a potential flow control technique. They were designed to match the mean separation bubble shape, which features a crest near the termination point of the incident shock wave. This crest generated expansion waves which counteracted the adverse pressure rise imposed by the shock wave and resulted in almost complete elimination of flow separation, which is a remarkable result. The bump also appeared to eliminate the low frequency bubble breathing oscillation. Additionally, it reduced the downstream boundary layer thickness by up to 10%. However, the bump effectiveness was found to be sensitive to the bump shape, and may fail at off design conditions. Further work will be required to examine the mechanisms by which these bumps eliminate separation and reduce the downstream boundary layer thickness.","abstract_html":"Oblique Shock Wave--Boundary-Layer interactions (oblique SBLIs) occur in many practical applications, such as in mixed compression supersonic jet intakes and transonic compressor cascades and can have significant detrimental effects on the downstream boundary layer, resulting in flow distortion, increased turbulent fluctuations, and pressure losses. They often occur near to a side-wall, such as in rectangular intakes, which introduces a side-wall boundary layer. At the intersection of the primary surface and the side-wall, a thick corner boundary layer is formed containing low momentum which separates readily at an adverse pressure gradient. The corner boundary layer separates further upstream than the primary separation and displaces the incoming flow. This generates corner compression and expansion waves which propagate into the primary interaction. Previous investigations have examined the effects of corner pressure waves on the interaction with the use of bluff block bodies placed in the streamwise corners of a supersonic wind tunnel which generate large corner separations. These blocks were shifted in the streamwise direction relative to the primary interaction in order to impart a varying corner wave influence. However, the corner compression and expansion waves are generated in relatively close proximity, with the result that the differing effects of these waves on the interaction could not be conclusively established. In this investigation conical corner bodies are used to generate corner compression and expansion waves with a clear physical separation between them. Experiments were run in a supersonic wind tunnel at Mach 2.5, with an incident shock deflection angle of 8°, and a Reynolds number based on the incoming boundary layer thickness of 1.8 x 10^5. The corner cones are placed in a range of streamwise locations to induce a varying corner influence on the interaction. This resulted in highly three-dimensional separation geometries in some cases and a wide range of centreline separation lengths, varying between 0.2 and 2.8 times the baseline case. A quasi-two-dimensional relationship between the local separation length and pressure along streamwise strips through the interaction was established. This is surprising given the strong three-dimensionality of these interactions. This relationship also confirms the qualitative observations of previous investigations that compression waves arriving over the interaction cause the separation length to increase, while expansion waves have the opposite effect. It was also found that corner waves arriving upstream of the interaction had a secondary influence on the separation length, while downstream waves had a greater than expected upstream influence. However, further work is required to explore the effects of up- and downstream waves on the interaction. Surface bumps were considered as an alternative method of introducing pressure waves into the interaction, and as a potential flow control technique. They were designed to match the mean separation bubble shape, which features a crest near the termination point of the incident shock wave. This crest generated expansion waves which counteracted the adverse pressure rise imposed by the shock wave and resulted in almost complete elimination of flow separation, which is a remarkable result. The bump also appeared to eliminate the low frequency bubble breathing oscillation. Additionally, it reduced the downstream boundary layer thickness by up to 10%. However, the bump effectiveness was found to be sensitive to the bump shape, and may fail at off design conditions. Further work will be required to examine the mechanisms by which these bumps eliminate separation and reduce the downstream boundary layer thickness.","abstract_has_math":false,"creators":["Missing, Timothy"],"institution":"University of Cambridge","degree_name":"Doctor of Philosophy (PhD)","degree_level":"Doctoral","degree_discipline":null,"degree_department":null,"school":null,"contributors":[],"advisors":["Babinsky, Holger"],"committee_chairs":[],"committee_members":[],"year":2025,"date_issued":"2025-01-01","date_published":"2025-01-01","updated_at":"2026-07-24T01:33:05Z","subjects":["Shock waves","Boundary layers","Shock wave boundary layer interactions","Supersonic flow"],"languages":[],"rights":[],"rights_urls":["https://www.repository.cam.ac.uk/bitstreams/9b260686-8271-4593-9adb-47ad431dfe23/download","http://purl.org/NET/rdflicense/allrightsreserved"],"identifier_entries":[]},"links":{"outbound_url":"https://doi.org/10.17863/CAM.120028","outbound_label":"DOI","outbound_source":"dc:identifier.doi"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor.advisor","label":"Advisor","values":["Babinsky, Holger"]},{"key":"dc:contributor.sponsor","label":"Sponsor","values":["My PhD research, tuition, and maintenance were all funded by the H2020-MSCA-ITN-2019 (Maria Skłodowska- Curie Innovative Training Networks) project titled TEAMAero (Grant Agreement No. 860909) The South African based Skye Foundation also supported me by covering costs associated with moving to the UK for the PhD, including my National Insurance and flights"]},{"key":"dc:creator","label":"Author","values":["Missing, Timothy"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date.issued","label":"Date","values":["2025-01-01"]},{"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/1810/387100"]},{"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":["Shock waves","Boundary layers","Shock wave boundary layer interactions","Supersonic flow"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:rights","label":"Dc Rights","values":["https://www.repository.cam.ac.uk/bitstreams/9b260686-8271-4593-9adb-47ad431dfe23/download","http://purl.org/NET/rdflicense/allrightsreserved"]},{"key":"dc:rights.embargodate","label":"Dc Rights Embargodate","values":["2026-07-16"]},{"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.120028"]},{"key":"dc:identifier.uri","label":"Identifier URI","values":["https://www.repository.cam.ac.uk/bitstreams/cfe53127-874a-4f22-8c75-51afdc423df3/download"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["Oblique Shock Wave--Boundary-Layer interactions (oblique SBLIs) occur in many practical applications, such as in mixed compression supersonic jet intakes and transonic compressor cascades and can have significant detrimental effects on the downstream boundary layer, resulting in flow distortion, increased turbulent fluctuations, and pressure losses. They often occur near to a side-wall, such as in rectangular intakes, which introduces a side-wall boundary layer. At the intersection of the primary surface and the side-wall, a thick corner boundary layer is formed containing low momentum which separates readily at an adverse pressure gradient. The corner boundary layer separates further upstream than the primary separation and displaces the incoming flow. This generates corner compression and expansion waves which propagate into the primary interaction. Previous investigations have examined the effects of corner pressure waves on the interaction with the use of bluff block bodies placed in the streamwise corners of a supersonic wind tunnel which generate large corner separations. These blocks were shifted in the streamwise direction relative to the primary interaction in order to impart a varying corner wave influence. However, the corner compression and expansion waves are generated in relatively close proximity, with the result that the differing effects of these waves on the interaction could not be conclusively established. In this investigation conical corner bodies are used to generate corner compression and expansion waves with a clear physical separation between them. Experiments were run in a supersonic wind tunnel at Mach 2.5, with an incident shock deflection angle of 8°, and a Reynolds number based on the incoming boundary layer thickness of 1.8 x 10^5. The corner cones are placed in a range of streamwise locations to induce a varying corner influence on the interaction. This resulted in highly three-dimensional separation geometries in some cases and a wide range of centreline separation lengths, varying between 0.2 and 2.8 times the baseline case. A quasi-two-dimensional relationship between the local separation length and pressure along streamwise strips through the interaction was established. This is surprising given the strong three-dimensionality of these interactions. This relationship also confirms the qualitative observations of previous investigations that compression waves arriving over the interaction cause the separation length to increase, while expansion waves have the opposite effect. It was also found that corner waves arriving upstream of the interaction had a secondary influence on the separation length, while downstream waves had a greater than expected upstream influence. However, further work is required to explore the effects of up- and downstream waves on the interaction. Surface bumps were considered as an alternative method of introducing pressure waves into the interaction, and as a potential flow control technique. They were designed to match the mean separation bubble shape, which features a crest near the termination point of the incident shock wave. This crest generated expansion waves which counteracted the adverse pressure rise imposed by the shock wave and resulted in almost complete elimination of flow separation, which is a remarkable result. The bump also appeared to eliminate the low frequency bubble breathing oscillation. Additionally, it reduced the downstream boundary layer thickness by up to 10%. However, the bump effectiveness was found to be sensitive to the bump shape, and may fail at off design conditions. 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They often occur near to a side-wall, such as in rectangular intakes, which introduces a side-wall boundary layer. At the intersection of the primary surface and the side-wall, a thick corner boundary layer is formed containing low momentum which separates readily at an adverse pressure gradient. The corner boundary layer separates further upstream than the primary separation and displaces the incoming flow. This generates corner compression and expansion waves which propagate into the primary interaction. Previous investigations have examined the effects of corner pressure waves on the interaction with the use of bluff block bodies placed in the streamwise corners of a supersonic wind tunnel which generate large corner separations. These blocks were shifted in the streamwise direction relative to the primary interaction in order to impart a varying corner wave influence. However, the corner compression and expansion waves are generated in relatively close proximity, with the result that the differing effects of these waves on the interaction could not be conclusively established. In this investigation conical corner bodies are used to generate corner compression and expansion waves with a clear physical separation between them. Experiments were run in a supersonic wind tunnel at Mach 2.5, with an incident shock deflection angle of 8°, and a Reynolds number based on the incoming boundary layer thickness of 1.8 x 10^5. The corner cones are placed in a range of streamwise locations to induce a varying corner influence on the interaction. This resulted in highly three-dimensional separation geometries in some cases and a wide range of centreline separation lengths, varying between 0.2 and 2.8 times the baseline case. A quasi-two-dimensional relationship between the local separation length and pressure along streamwise strips through the interaction was established. This is surprising given the strong three-dimensionality of these interactions. This relationship also confirms the qualitative observations of previous investigations that compression waves arriving over the interaction cause the separation length to increase, while expansion waves have the opposite effect. It was also found that corner waves arriving upstream of the interaction had a secondary influence on the separation length, while downstream waves had a greater than expected upstream influence. However, further work is required to explore the effects of up- and downstream waves on the interaction. Surface bumps were considered as an alternative method of introducing pressure waves into the interaction, and as a potential flow control technique. They were designed to match the mean separation bubble shape, which features a crest near the termination point of the incident shock wave. This crest generated expansion waves which counteracted the adverse pressure rise imposed by the shock wave and resulted in almost complete elimination of flow separation, which is a remarkable result. The bump also appeared to eliminate the low frequency bubble breathing oscillation. Additionally, it reduced the downstream boundary layer thickness by up to 10%. However, the bump effectiveness was found to be sensitive to the bump shape, and may fail at off design conditions. 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