Application of Modern Design of Experiments to CARD Thermometry in a Supersonic Combuster

We have applied formal experiment design and analysis to optimize the measurement of temperature in a supersonic combustor at NASA Langley Research Center. We used the coherent anti-Stokes Raman spectroscopy (CARS) technique to map the temperature distribution in the flowfield downstream of an 1160 K, Mach 2 freestream into which supersonic hydrogen fuel is injected at an angle of 30 degrees. CARS thermometry is inherently a single-point measurement technique; it was used to map the flow by translating the measurement volume through the flowfield. The method known as “Modern Design of Experiments” (MDOE) was used to estimate the data volume required, design the test matrix, perform the experiment, and analyze the resulting data. MDOE allowed us to match the volume of data acquired to the precision requirements of the customer. Furthermore, one aspect of MDOE, known as response surface methodology, allowed us to develop precise maps of the flowfield temperature, allowing interpolation between measurement points. An analytic function in two spatial variables was fit to the data from a single measurement plane. Fitting with a cosine series bivariate function allowed the mean temperature to be mapped with 95% confidence intervals of ±30 K, comfortably meeting the precision requirement of ±50 K specified prior to performing the experiments. We estimate that applying MDOE to the present experiment saved a factor of five in data volume acquired, compared to experiments executed in the traditional * Research Scientist, Member AIAA ** Senior Research Scientist, Member AIAA # Associate Professor, Senior Member AIAA Copyright © 2002 by the American Institute of Aeronautics and Astronautics, Inc. No copyright is asserted by the United States under Title 17, U. S. Code. The U. S. Government has a royalty-free license to exercise all rights under the copyright claimed herein for Government Purposes. All other rights are reserved by the copyright holder. manner. Furthermore, the precision requirements could have been met with less than half the data acquired.