A hybrid probabilistic model was developed and used to investigate a generic scramjet engine at flight conditions (Mach 8, 30 km altitude). To assess the robustness of the design, uncertainties in boundary conditions and modelling were considered. The full-system model is composed of three parts, which were modelled separately: inlet with isolator, combustion chamber and nozzle. The inlet and the nozzle were resolved using two-dimensional calculations solving the Reynolds averaged Navier Stokes equations, while the combustion chamber modelling was based on an one-dimensional stream tube approach. Flight properties and injection parameters were considered aleatoric in nature. Uncertainties introduced by different averaging approaches at the model interface were presumed to be epistemic. The uncertainties were propagated using probabilistic collocation if feasible and Monte Carlo simulation if necessary. The more recent probabilistic collocation approach allows a reduction of the necessary number of evaluations. Hence, a more detailed model can be employed. However, as this polynomial chaos approach is only valid for smooth transformations, it fails to predict singular hazardous events, e.g. discontinuities such as thermal choking of the combustor. To consider these events, a Monte Carlo simulation had to be applied. The hybrid model and the full probabilistic collocation model showed equivalent results. But the hybrid model acquired additional information at overall lower calculation expanses.
CEAS Aeronautical Journal – Springer Journals
Published: May 29, 2018
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