TECHNOLOGY AREA(S): Air Platform
OBJECTIVE: Develop hardware, techniques, and standards required to improve the calibration of sensors used to measure high speed airflow.
DESCRIPTION: Scientific understanding of the multi-physics underlying the interaction of high speed flows and structural response of airframes to aerothermal effects, shocks, and high frequency flow oscillations depends on our ability to measure and model complex flow fields as they pass over and around the airframe. These airframes may vibrate, flex, and ablate during ground or flight test, leading to additional flow field perturbations and dynamical changes. While current and next generation sensors and instruments may have the ability to measure various parameters of interest for characterizing airflow and structural responses, understanding these measurements and relating them properly to physics-based models depends on accurate instrument calibration throughout the measurement period. The Air Force is looking to improve calibration capabilities for instruments that measure flow and structure behavior in high speed airflows. Of particular interest is the flow regime where aerothermal effects are present, generally at speeds of Mach 5 and higher. At these speeds, high frequency oscillations in the incoming airflow are critical to the flow development around the vehicle so improved calibration for instruments capable of making measurements up to several MHz are of high interest. Responses that address the calibration of instruments commonly employed for use in high speed wind tunnels are sought, but proposals addressing the calibration of next generation instruments may be considered for sensors that have been successfully demonstrated and ready to enter the commercial market. Although sensors that measure pressure are of high interest, sensors that measure temperature, heat flux, wall shear stress, or paints that are sensitive to temperature or pressure at high time resolution will also be considered. In some cases the sensing system may rely on external sources, such as particles for PIV or light for Schlieren, for the measurement to be made, so the calibration process may need to take source generation and uniformity into account. Calibration may also be sensitive to instrument gain, electrical junctions, line delays, and electronics temperature changes induced by sensor current changes, so comprehensive approaches are encouraged. The approach should include evaluation of the effects of known extraneous environmental inputs such as mechanical vibration and temperature as well as off-axis response when applicable. Proposers must discuss plans for testing in wind tunnels or other appropriate facilities capable of Mach 5+ in the Phase 1 proposal, although testing and detailed test plans will not be required until Phase 2. The Phase 1 proposal team must include members with the necessary expertise to conduct experimental tests safely at these facilities, discuss this expertise in the proposed approach, and demonstrate this when the credentials of key personnel. In Phase 1 proposers shall identify class of sensors and instruments, document current industry standard for their calibration, develop new or improved calibration concepts and techniques, and demonstrate, measure, and quantify potential for calibration improvements for 2 or more instruments in this class. In Phase 2 proposers shall develop calibration equipment, processes, and techniques for this class of instruments. Document calibration process and prepare it to become a new industry standard. Demonstrate and deliver NIST traceable calibration equipment, processes, techniques, data, and documentation to an Air Force facility.
PHASE I: Identify class of sensors and instruments, document current industry standard for their calibration, develop new or improved calibration concepts and techniques, and demonstrate, measure, and quantify potential for calibration improvements for 2 or more instruments in this class.
PHASE II: Develop calibration equipment, processes, and techniques for this class of instruments. Document calibration process and prepare it to become a new industry standard. Demonstrate and deliver NIST traceable calibration equipment, processes, techniques, data, and documentation to an Air Force facility.
PHASE III: Calibration equipment, instruments, and services may be offered to government, universities, and industry.
1. Dennis Berridge. Generating Low-Pressure Shock Waves for Calibrating High-Frequency Pressure Sensors. PhD thesis, School of Aeronautics and Astronautics, Purdue University, December 2015.
2. Eric C. Marineau. Prediction methodology for 2nd mode dominated boundary Layer transition in hypersonic wind tunnels. Paper 2016-0597, AIAA, January 2016.
3. Adam M. Hurst, Timothy R. Olsen, Scott Goodman, Joe VanDeWeert, and Tonghuo Shang, An Experimental Frequency Response Characterization of MEMS Piezoresistive Pressure Transducers, Proceedings of ASME Turbo Expo 2014: Turbine Technical Conference and Exposition, GT2014, June 16, 2014, Dusseldorf, Germany.
4. National Institute of Standards and Technology (NIST), Traceability - NIST Policy and Supplementary Materials, Retrieved from http://www.nist.gov/traceability/.
KEYWORDS: Improved Instrument Calibration, Wind Tunnel, Flight Test, High Frequency Oscillations, High Speed Turbulent Flow, Structural Response, Aerothermal, Pressure, Temperature, Heat Flux