Effect of turbulence model closure coefficient uncertainty on scramjet flow field analysis

“The numerical modeling of supersonic combustion ramjet (scramjet) engine flow paths plays an important role in the design of hypersonic air-breathing propulsion systems. Due to the complexity of the flow field physics and limited experimental data, numerical models possess uncertainties which should be addressed to improve the prediction accuracy of the simulations. In this study, the effect of turbulence model closure coefficient uncertainty on the Reynolds-averaged Navier-Stokes solution of a scramjet isolator and scramjet strut fuel injector flow field is investigated with an uncertainty quantification and sensitivity analysis study for commonly used turbulence models. Turbulence models considered in this work are Menter-BSL, Menter-SST, Spalart-Allmaras, and Wilcox-2006 k-l. Simulations were carried out using NASA’s VULCAN flow solver. Nonintrusive polynomial chaos theory was used for efficient propagation of uncertainty, and Sobol indices were utilized to quantify the global non-linear sensitivity of various solution metrics to the variation of each closure coefficient. The scramjet isolator study considered the shock location, skin friction coefficient, and integrated axial shear force as output metrics of interest. The output metrics of interest for the strut fuel injector study included the integrated quantities of mixing efficiency, circulation, total pressure recovery, and one-dimensional Mach number, as well as the pointwise vorticity and eddy viscosity distributions, and were evaluated at three crossflow planes. The results obtained were compared to available experimental data as well as to previous work focusing on relevant flow problems and other sources of solution uncertainty. Influential sets of closure coefficients were identified for each turbulence model, with the Kármán and diffusion constants being the most prominent. The results presented in this work are expected to assist future efforts aimed at reducing the uncertainty in the numerical design of scramjet engine components through the identification of closure coefficients and physical aspects of the flow that warrant further investigation”--Abstract, page iii