High-Bandwidth High-Resolution Sensor for Hypersonic Flows

We propose to develop a miniature a.c. driven, weakly-ionized plasma anemometer for measurements at hypersonic Mach numbers. The design will be based on earlier work by Vrebalovich (1954) who developed an a.c. glow-discharge anemometer and demonstrated itssensitivity to mean and dynamic mass-flux variations for Mach numbers between 1.3 and 4. The advantages of the plasma anemometer are that it requires no frequency compensation up to its a.c. carrier frequency, has an amplitude modulated output that hasexcellent common-mode rejection with a signal-to-noise that is much better than a hot-wire, is robust with no sensor elements to break, can have a small spatial volume, and is insensitive to temperature variations making calibration easier thanthermal-based sensors. The Phase I effort will consist of designing and fabricating the plasma probe and electronics, bench testing to determine its durability over time, calibration of the sensor output with respect to mean and rms mass flux variations,and determining its frequency response limits. This work will utilize facilities in the Notre Dame Center for Flow Physics and Control, including a heated compressible Mach number jet, and a tri-sonic wind tunnel. If time permits during Phase I, orotherwise in a Phase II effort, we would also plan to use the AFRL Hypersonic Facility for further assessment and calibration. This work will be a natural outgrowth of our extensive experience in developing plasma actuators for flow control applications,which rely on the same physics as the plasma anemometer, and in the calibration and use of sensors in high Mach number flows. Research performed during Phase 1 and Phase II study will result in the development of flow control devices, flow measurementinstrumentation especially the high-resolution sensor for hypersonic flows, and a database for the understanding of hypersonic flow phenomena. Weakly ionized plasmas have shown great promise as flow control devices. This research will allow us to quantifytheir use as a sensor. The implication of this is that the same plasma device can be used to simultaneously operate as an actuator and sensor. No other actuator or sensor has this dual capability. This would allow compact packaging of actuators/sensorsfor feedback control that would be unprecedented in flow-control applications.The developed hardware and software will also have commercial applications to civilian space launch and high-speed vehicles. The proposed approach in implementing state-of-the art instrumentation for hypersonic flows will significantly advance theunderstanding of hypersonic aerodynamics. The research and instrumentation developed under the current STTR program will be extended to application in high-enthalpy hypersonic ground-test facilities and possible bio-medical applications.