Diagnostic Modelling of an Expansion Tube Operating Condition for a Hypersonic Free Shear Layer Experiment

Computational simulations of the AIR-1 test condition in the University of Illinois’ Hypervelocity Expansion Tube were conducted to verify facility operation and to obtain free stream properties that are otherwise difficult to measure. Two types of simulation were undertaken. The first was a one-dimensional simulation of the entire facility and the second was a hybrid simulation, combining a one-dimensional simulation of the shock tube section with a two-dimensional simulation of the acceleration tube. The one-dimensional simulation matched the experimental data well, however the two-dimensional simulation did not initially match the experimental measurements of shock speed and test gas pitot pressure. Further investigation showed the shock speed discrepancy was consistent with air contamination into the acceleration tube and subsequent two-dimensional simulations assuming 10% air contamination showed reasonable agreement with experimental data. Using data taken from the two-dimensional simulation of the expansion tube as a transient inflow condition, modelling was undertaken of a free shear layer experiment being conducted in the facility. Results from equilibrium, finite rate, and perfect gas models were compared. The finite rate simulation provides the best agreement with experimental Schlieren images, with the simulation capturing the major flow structures seen in experiments.