TECHNOLOGY AREA(S): Air Platform
OBJECTIVE: Develop robust sensors and an efficient data reduction methodology to obtain temporally and spatially resolved surface temperature and heat flux measurements on test articles in blowdown and continuous hypersonic wind tunnels
DESCRIPTION: The Air Force needs robust surface heat flux sensors that provide spatially resolved surface temperature and heat flux measurements on test articles in blowdown and continuous hypersonic wind tunnels. Such measurements are needed to fully understand the state of the boundary layer and provide high quality transitional and turbulent heat transfer data for designing hypersonic vehicles and validating computations of the same flows. Critical areas where heat flux measurement are needed include leading edges with small radii from 5 mm to 15 mm, control surfaces, and vehicle base. The thin film sensors that have been successfully used in impulse facilities  have yet to be successfully deployed in blowdown hypersonic wind tunnels which have a total run time between 0.5 and 5 seconds. Blowdown facilities require sensors that minimize surface hot spots and provide an improved durability to erosion since test times in blowdown facilities are typically between 10 and 1000 times longer than in impulse facilities. The longer test time also implies that multidimensional heat conduction effects can be present in areas with large lateral temperature gradients such as leading edges. The sensors and data reduction methodology need to provide both surface temperature and heat transfer in standard stainless steel test articles and account for lateral heat conduction and temperature dependent thermal properties. The frequency response needs to be above 500 kHz to characterize flow instabilities and turbulent spots. High frequency measurement of 2nd mode instabilities have been successfully performed with Atomic Layer Thermopile (ALTP) sensor [2, 3] and survivability on probes and heat shields has been demonstrated in blowdown wind tunnels . However, ALTP sensors have a large footprint which prevents close sensor spacing and measurements in area of small surface curvature. The new sensors need to provide multiple point measurements on small leading edge radii where multidimensional conduction effects can be significant over the test period. For leading edges, substrate materials with a lower thermal conductivity such as MACOR might be acceptable, but sensor integration must provide well defined boundary conditions for data reduction. The sensors must sustain surface temperatures as high as ~1000 K which is a requirement for leading edges in typical blowdown hypersonic tunnels and over the test article surface in continuous hypersonic tunnels. In continuous tunnels, heat transfer measurements are performed by injecting the test articles for multiple short duration segments (with retraction and cool down periods). However, the sensors must sustain prolonged hypersonic flow during force-and-moment testing (aerodynamic test segments) during which the test article surface temperature approaches the flow recovery temperature. In Phase 1, proposers shall evaluate the sensor requirements and perform numerical or analytical design studies. In addition, a prototype sensor and data reduction methodology shall be developed. Finally, the proposers shall perform primary bench top calibrations and small scale testing on a well-defined test configuration subjected to a well-characterized hypersonic flow. In Phase 2, proposers shall further refine the sensor design and implement an efficient data reduction methodology. Detailed static and dynamic calibrations shall be performed to demonstrate the sensor frequency response and absolute heat transfer precision and accuracy. Finally, the proposer shall demonstrate the sensor ruggedness, precision, accuracy and frequency response in a representative hypersonic flow environment in a pertinent experimental facility.
PHASE I: Evaluate the sensor requirements, perform numerical/analytical design studies, and develop prototype sensors, test article and data reduction algorithms. Perform preliminary bench top calibrations and testing in a small scale hypersonic facility under a well characterized flowfield.
PHASE II: Develop sensors and efficient data reduction methodology. Demonstrate and deliver sensors, signal conditioning hardware, data reduction, and documentation to a pertinent hypersonic experimental facility. Demonstrate the sensor ruggedness, precision, accuracy and frequency response in a representative hypersonic flow environment in a pertinent experimental facility
PHASE III: Validated sensors and data reduction software may be offered to government, universities, and industry.
1. Timothy Wadhams, Michael Holden, Matthew Maclean, Charles Campbell, Experimental Studies of Space Shuttle Orbiter Boundary Layer Transition at Mach Numbers from 10 to 18, AIAA Paper 2010-1576
2. Tim Roediger, Helmut Knauss, Boris V. Smorodsky, Malte Estorf, Steven P. Schneider, Instability Waves Measured Using Fast-Response Heat-Flux Gauges, Journal of Spacecraft and Rockets, Vol. 46, No. 2, pp. 266-273, 2009
3. Michael A. Kegerise, Shann J. Rufer, Unsteady Heat-Flux Measurements of Second-Mode Instability Waves in a Hypersonic Boundary Layer, AIAA Paper 2016-0357
4. Eric Marineau, Daniel Lewis, Michael Smith, John Lafferty, Molly White, Adam Amar, Investigation of Hypersonic Laminar Heating Augmentation in the Stagnation Region, AIAA Paper 2013-308
KEYWORDS: Heat Flux Sensor, Temperature Sensor, Hypersonic Flow, Hypersonic Wind Tunnel, Turbulence In Hypersonic Flows, Boundary-layer Transition, Heat Conduction