Diagnostic modelling of an expansion tube operating condition

Computational simulations of an expansion tube were conducted to estimate flow parameters and verify experimental uncertainties. Two types of simulations of the complete facility were undertaken: a one-dimensional simulation, and a hybrid simulation where a one-dimensional simulation of the shock tube section was coupled with a two-dimensional simulation of the acceleration tube. Good agreement between the one-dimensional simulations and experiments were obtained in the shock tube portion of the facility. In the acceleration section, initial two-dimensional simulations did not match the experimentally measured pitot pressure and showed a discrepancy in the shock speed. Further studies examined how the accelerator gas composition affected shock speed, static pressure and pitot pressure levels in expansion tube operation. Subsequent two-dimensional simulations, using an 8% level of air contamination in helium, showed reasonable agreement with experimental data. This prediction of air contamination was later confirmed with experimental measurements of the air partial pressure before operation.