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Title: Unsteadiness of shock wave boundary layer interactions across multiple interaction configurations and strengths
Author: Threadgill, James
ISNI:       0000 0004 6346 9738
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2017
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Shock Wave Boundary Layer Interactions (SWBLIs) represent complex flow phenomena that remain poorly understood despite their prevalence on high-speed vehicles, in part due to their complicated underlying physics. In particular, the mechanisms that drive the high-amplitude, low-frequency unsteadiness within the interaction have perplexed researchers for many years while remaining a limitation to vehicle performance and a potential danger to airframe integrity. This investigation has specifically examined the influence of interaction strength and configuration type on the characteristic unsteady behaviour that describes the flow environment. Until now, researchers have typically focused on testing a specific configuration in a given test facility. This approach can obscure meaningful conclusions that may be drawn due to the interference of the test environment. The present research effort therefore tackles this flaw by assessing flow behaviours across a range of SWBLIs, all tested within a common environment. Four strengths of oblique shock reflection interactions and two strengths of compression ramp interactions have been assessed and compared. Experiments have been conducted in the Imperial College Supersonic Wind Tunnel with a Mach 2 turbulent incoming boundary layer with momentum thickness Reynolds number of 8000. Using a combined approach of synchronised PIV and fast-response wall-pressure measurements the unsteady elements to the interactions have been investigated. The spectral evolutions of unsteady wall-pressure disturbances are assessed throughout each of the interactions. Results confirm that the high-frequency component of the separation shock spectral content is common across all interactions. Meanwhile, low-frequency amplitudes scale with the interaction length, acting to decrease the characteristic frequency used to describe such motion when the interaction strength is increased. Instantaneous shock structures have also been identified which confirm the presence of two unsteady mechanisms governing the dynamics of the separation shock: rotation and translation. Quasi-steady modelling of these mechanisms indicates how their relative dominance varies with interaction strength and configuration type. This body of work represents a unique assessment of valuable data that is crucial to the development of unsteady SWBLI understanding.
Supervisor: Bruce, Paul Sponsor: Engineering and Physical Sciences Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral