Hypersonic Propulsion: Improvements in Controls and Instrumentation

ABSTRACT: Among the technical challenges associated with current Air Force scramjet technology development is coupling between the combustor and isolator that leads to isolator unstart. Performance is currently restricted because the engine is not actively controlled. While simple passive techniques such as cavities for shock capture exist, they result in increased drag. We propose a closed-loop control scheme that seeks to actively isolate the inlet from the combustor to prevent unstart while monitoring and minimizing the drag in the inlet using flow control. The shock trapping scheme is based on a cavity in the isolator section and the flow control system consists of arc filament plasma actuators coupled with skin friction sensors. When there is potential for unstart, the actuators will make the cavity a high drag cavity, which would act as a shock trapping device. In normal operation, the actuators will be adjusted to minimize the drag of the cavity. The skin friction sensors that are based on an existing Surface Stress Sensitive Film sensor hardened to operate in high enthalpy flows. The flow control scheme is based on a class of high amplitude and high bandwidth plasma actuators called localized arc filament plasma actuators. BENEFIT: Surface Stress Sensitive Films are being investigation for a variety of applications in aerodynamics, hydrodynamics, and biomedical research. Skin friction is a quantity of interest in many aerodynamics applications such as validation of CFD, and investigation of hypersonic inlets. A point version of this sensor could be used for both ground test and flight test measurements of skin friction. Other applications include a sensor for feedback in closed loop flow control. The S3F sensor has recently been used to detect shear forces on tires and a means of using the system for predictive maintenance of fleet vehicles is underway. The sensor also has use in biomedical applications include ongoing research for identification and correlation of shear on the foot of diabetics. The formation of bed sores is believed to be related to shear stress, and therefore this would be a similar application of the technology. Other biomedical applications include shear stress on surfaces of artificial implants such as stints, hearts, valves, and assist pumps