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 K 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
equivalence ratio 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.