Dual-Mode Scramjet Combustor: Numerical Sensitivity and Evaluation of Experiments

摘要

Experiments were performed at the Air Force Research Laboratory's Propulsion Directorate (AFRL/RZ) in Research Cell 22 (RC22). Twelve cases from the experiment were computationally analyzed and each case varied in either engine operating condition and/or combustor configuration. Initial computations were performed on all twelve cases to establish a baseline computational approach. Computations were performed on one of the cases to test sensitivity to turbulent Schmidt number, reaction rate, and grid resolution. Improvements to the baseline analysis using the results from the sensitivity analyses were extended to two additional cases. It was shown that adjustments in Schmidt number, reaction rate, or grid refinement improved the agreement with experimental data for two cases relative to the baseline results, but worsened agreement for the third case. It was left undetermined that grid refinement was a better approach to improving the baseline analysis as compared to calibrations in Schmidt number and/or reaction rate. Improvement to the grid using local refinement in regions with chemical reactions produced better results for one case and was computationally less expensive than globally refining the grid. Negligible differences were shown between results that were obtained using wall functions with Y+ value as high as 38 or results obtained using wall integration with Y+ values around one. Negligible differences were shown between periodic results that were obtained by averaging results using either a constant CFL or a constant time step. CFL-averaging a result using the constant CFL approach was 5.4 times less computationally expensive than using the constant time step approach. Computations showed that 2.53-lbm/sec. of air leaked into the exhauster housing at the exit of the combustor in RC22's test apparatus.