Abstract
Modelling the complete flow physics and chemical kinetics of supersonic combustion is a particularly complex and daunting task that requires significant computational resources. To foster performance evaluation tools for future hypersonic vehicles, developing accurate yet computationally efficient solution methods is of great importance. In this work, a new subgrid combustion model for large eddy simulations is derived and used in a three-dimensional in-house flow solver to provide simulations of experimental scramjet ground tests. In particular, this paper introduces a hybrid model closure with the reaction-rate approach to close the filtered chemical source terms in the governing equations for species mass fractions and total energy. The model developed here makes use of a linear bridging function, depending on the segregation rate of the mixture fraction, between a resolved contribution issued from a perfectly stirred reactor (PSR) estimation, and a subgrid-scale (SGS) contribution where a closure that approximates the Lagrangian trajectory in the composition space is retained. The new model considers the effect of fluctuations of compositions and can be extended to take into account, for example, the fluctuations of temperature. The new approach is tested using a hydrogen-fueled scramjet combustor from circular injector into a Mach 2 vitiated airflow for total pressure and temperature of 0.40 MPa and 1695 K, respectively. The selected operating conditions are representative of the LAPCAT-II dual-mode ramjet/scramjet combustion. Chemistry is described using a four-step reduced mechanism. The results obtained with the present modelling proposal are compared to those issued from numerical simulations performed with the quasi-laminar chemistry or PSR approach. These results do show that, even for a highly resolved computational mesh, the effects of composition fluctuations remain significant, especially in the vicinity of the injection where the SGS fluctuations of the scalar field are non-negligible.