University of Cambridge
Sidewall effects in compression corner shock-wave/boundary-layer interactions
Abstract
dc:description.abstractStreamwise corners are a common three-dimensional geometric feature encountered in supersonic flows, appearing in wing-body junctions, in rectangular cross sectioned inlets and research wind tunnels. When a shock wave boundary layer interaction (SBLI) occurs in a rectangular cross sectioned duct, the streamwise corner flows tend to separate, resulting in highly three-dimensional behaviour in the sidewall region. These corner separations have been seen to influence the ‘quasi-2D’ primary SBLI far away from the sidewalls for the oblique shock reflection. The mechanism for these ‘corner effects’ is not fully understood, and it is not known if they are present in other supersonic SBLIs such as the compression corner. To investigate how corner effects may influence the quasi-2D behaviour of the compression corner, experiments are conducted in a rectangular cross sectioned wind tunnel. Tests are carried out at Mach 1.5, 2.5 and 3.5 on separated turbulent compression corner SBLIs at ramp angles of 11◦, 20◦, and 23◦. The flow-field is examined using schlieren photography, oil-flow visualisation, Pressure Sensitive Paint, and Laser Doppler Velocimetry. The flows are all separated in the baseline case. The Mach 2.5 and 3.5 baseline cases both show quasi-2D separations for the majority of the tunnel span, while the Mach 1.5 baseline shows significant three-dimensionality as a result of corner effects. The size and scale of corner separations are manipulated by placing rectangular blocks into the streamwise corners. Depending on the location of the blocks, the location and scale of streamwise corner separation changes. The streamwise corner separations, through displacing the external supersonic flow, are found to produce waves. These corner waves typically consist of a corner shock followed by expansions. The waves are seen to propagate far from the sidewalls and impinge on the primary interaction. We find that the size and structure of the primary separation produced by the compression corner is influenced by the location and scale of corner separation. The pattern of both corner shocks and expansions makes it difficult to identify how each wave type influences the interaction. To isolate the effect of corner shocks on the SBLI, quarter cones are placed into the streamwise corners. These cones produce a simple wave structure consisting purely of a corner shock followed by conical compressions. When theseshocks impinge on the central interaction, the centreline separation length increases with increasing corner shock strength. Examining streamwise pressure traces reveals a common mechanism by which corner waves influence the interaction for all three test Mach numbers. We find that the pressure rise to separation is not influenced by corner waves, however the reattachment pressure rise is. Importantly, it is seen that each streamwise strip of flow behaves as if it were locally quasi-2D, the local separation length depending only on the primary interaction pressure rise in the streamwise direction. Depending on the nature of the corner waves and the location where they ‘arrive’ along a strip they can have different effects on the local separation length. Corner waves that arrive upstream or downstream of the interaction exert no influence. We suggest that when a corner wave arrives in the plateau region it is unable to support the pressure rise, and it is added to the reattachment pressure jump. For a corner shock this increases the required reattachment pressure rise, increasing the separation length, with the opposite occurring for corner expansions. From these two-dimensional ideas a predictive model is formulated and used to successfully predict how corner effects influence the size and shape of separations produced by both the compression corner and oblique shock reflection SBLIs. Initial work has been carried out to investigate corner effects on the low frequency unsteadiness of the compression corner SBLI. The low frequency peak was resolved using high speed schlieren and point Laser Doppler Velocimetry measurements. It was found that the intensity of the low frequency peak can be influenced by the location and scale of corner separations, in a way that tracks the size of the central separation.
Degree
thesis:*- Name dc:type.qualificationname
- Doctor of Philosophy (PhD)
- Level dc:type.qualificationlevel
- Doctoral
- Grantor dc:publisher.institution
- University of Cambridge
- Year dc:date.issued
- 2023
Author and committee
dc:creator, dc:contributor.*- Author dc:creator
-
- Williams, Rhys
- Advisor dc:contributor.advisor
-
- Babinsky, Holger
Subjects
dc:subject × 12Rights
dc:rightsIdentifiers
dc:identifier.*- DOI dc:identifier.doi
- https://doi.org/10.17863/CAM.108720
- OAI identifier oai:identifier
- oai:www.repository.cam.ac.uk:1810/368567