Experimental Performance Characterisation and Measurement of Unstart Force on a Scramjet Intake across the Operational Envelope

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This project falls within the EPSRC Fluid dynamics and aerodynamics research area.IntroductionHypersonic vehicles travelling at over Mach 5 are in development for access to space, civil transportation, and defence purposes. To increase mission capability, air-breathing engines are favoured over rocket-based systems as they do not carry any oxidiser. For Mach 5 and over, the only viable systems are Rotary Detonation Engines (RDEs) or Supersonic Combustion Ramjets (SCRamjets). These both rely upon supersonic intake performances to compress the incoming air with minimal losses. Most intakes are designed assuming steady-state operation at a single design point yet are expected to operate over a range of flight conditions and attitudes. Transient variations adversely affect the overall performance of the intake, which can result in either engine flame out or unstart. During the development of the Lockheed SR-71 'Blackbird' aircraft, the unstart of a single engine would produce a significant yawing moment that in some instances caused the loss of the vehicle. There has been significant academic investigation with the goal of developing predictive control strategies to mitigate or prevent unstart. However, there is limited experimental data on the magnitude of force generated during unstart for scramjet inlets. It remains an open research question as to whether the forces generated are sufficient to cause loss of vehicle or adjacent-engine failure in multi-engine configurations. Project AimThe primary aim of the proposed DPhil project is to experimentally investigate the forces imparted to a vehicle during the un-start of a scramjet intake over a range of conditions. Additionally, the project will explore the influence of vehicle attitude on intake performance and differences arising between low and high-enthalpy testing.MethodologyThis study will be primarily experimental, using the Oxford High-Density Tunnel (HDT) for low-enthalpy tests and the University of Queensland reflected shock tunnel facility X3R for high-enthalpy tests. Additionally, the project will use a device called MassCap, which is a novel mass flow measurement and mechanical back-pressurisation device developed at Oxford specifically for high-speed intake testing in short-duration facilities.The bulk of the first year will be dedicated to the design of an intake. During the second year, the experimental intake model will be manufactured, and experimentally characterised in the HDT. This facility will be operated in PALM mode (a mode with extended test times) to enable the start/un-start cycle to be investigated. In the third year of the DPhil, experiments using the same model will be undertaken in the University of Queensland shock tunnel facility at flight enthalpy conditions. In this way, changes in the inlet performance due to high enthalpy effects may be examined, providing a better assessment of the performance in flight.The inlet performance will be characterised throughout the flight envelope. Measurement of the axial force induced during inlet unstart will be unique and offer insight into the impact on the overall vehicle. The change in performance with attitude, sensitivity of the intake to unstart and self-starting capability will also be investigated. High-speed Schlieren videography will be used to examine the external shock structure during starting/un-starting and the use of pressure-sensitive paint and infrared thermography to provide an improved spatial resolution of the surface pressure and heat flux (respectively) will be explored. Throughout the project, the student will interact with other student and staff members within the Oxford hypersonics groups as well as external academic, government, and industry partners, such as at the University of Queensland Centre for Hypersonics.