High-Order Flux Reconstruction for the Implicit Large Eddy Simulation of an Axisymmetric Scramjet Combustor

The high-order Flux Reconstruction method is used to conduct large-eddy simulations of an axisymmetric inlet-isolator-combustor configuration experimentally tested in the University of Illinois’s ACT-II arc-heated combustion tunnel and numerically investigated with North Carolina State University’s REACTMB solver. A divergence-based indicating and modal filtering scheme is used for shock capturing, aided by a boundedness filter for additional solution stabilization. A 7-species 3-step reaction mechanism developed at the Air Force Research Laboratory is used in these calculations. An isothermal wall of 375 Kelvin is assumed. The Flux Reconstruction method, equipped with the correction functions that recover a Discontinuous Galerkin discretization, was run at varying polynomial orders from linear P1 elements to quartic P4 elements. It is shown that P-scaling is an effective technique for the enhanced resolution of small-scale turbulent structures, with the present method comparing favorably to high-order finite volume methods while operating on a coarser discretization. The shock-capturing method presented is not found to scale well with polynomial order, and as such compares poorly with the previous results. The stable ram-mode combustion with an ER of 1.24 was unable to be achieved, instead leading to unstart of the flowpath. At lower polynomial orders, P1 and P2, a rotating detonation wave is formed in the region downstream of the injectors prior to the unstart event. Higher polynomial orders, P3 and P4, do not form a detonation wave but show an intermittent combustion operation with multiple, smaller, pressure waves present in the powerhead region.