Aerothermal Measurement Improvements using Coaxial Thermocouples at AEDC Hypervelocity Wind Tunnel No. 9

The Arnold Engineering Development Center (AEDC) Hypervelocity Wind Tunnel No. 9 Facility has played a key role in the development of hypersonic vehicles for over 30 years, providing high-quality aerodynamic and aerothermal test data covering high Mach number and high Reynolds number flight simulations. Over the last ten years, the fidelity of computational fluid dynamics tools has advanced to the point that higher accuracy validation data are needed. Therefore the experimental community must also continue to evaluate the measurement techniques utilized to provide these data, modify the techniques whenever necessary, and develop new cutting edge techniques to ensure that the highest data quality is available to support the advanced code validation efforts. An example of this process occurred recently at Tunnel 9 during two aerothermal test programs. During these tests, pretest aerothermal computations matched the general data trends reasonably well; however, an approximate 15-percent bias between the data and the computations was observed. An effort was initiated to calibrate the as-installed coaxial thermocouple gage versus a National Institute of Standards and Technology (NIST)-traceable heat-flux standard. This paper discusses the efforts taken to date and immediate recommendations to investigate the possible source of the discrepancy.