One Dimensional Modelling and Sensitivity Analysis for the ACT-II Facility

This work presents a detailed analysis of the chemical and thermal non-equilibrium phenomena in high enthalpy flows generated in the Arc-heated Combustion Test-rig II (ACT-II) facility at UIUC. To this aim, a high-fidelity model accounting for the multi-temperature finite rate nature of the chemical processes is implemented in a quasi-one-dimensional flow solver and used to describe: energy deposition, mass addition, and acceleration of flow in the nozzle of the ACT-II tunnel. Robust estimation of gas composition at the test section entrance is performed via a global sensitivity analysis leveraging surrogates based on a Polynomial Chaos Expansion (PCE) to alleviate the computational burden. The most influential parameters are determined via computation and analysis of Sobol’ indices. Results show that the flow is found in local thermodynamic equilibrium at the nozzle inlet and non-equilibrium effects occur mainly inside the nozzle. The composition is extremely sensitive to the energy deposition, three-body recombination of oxygen, and Zel’dovich reactions.