Assessment of a hybrid RANS/LES simulation method and URANS method in depicting the unsteady motions of flow structures in a scramjet combustor

A scramjet combustor is simulated using both a hybrid Reynolds averaged Navier-Stokes (RANS)/large eddy simulation (LES) method, namely zonal detached eddy simulation (ZDES), and unsteady RANS (URANS) method to conduct an assessment of their abilities in depicting the unsteady motions of flow structures in the scramjet combustor. Although ZDES and URANS present a similar ability with regard to calculating the mean variables, they present distinct differences concerning the ability to capture the unsteady motions of the flow structures. The ZDES case successfully captures the unsteady motions of the shock structures. The resolved flow is comprised of a series of oscillating cycles that mixes strong cycles and weak cycles, and one or more strong cycles are followed by one or more weak cycles. In strong cycles, the oscillating amplitude of the pressure is large and the duration of cycle is long. The range of the motion of shock structures is large, and a Mach disc is formed when the shock structures move upstream. In weak cycles, the oscillating amplitude of the pressure is small and the duration is short, and no Mach disc appears throughout a cycle. All of these coincide fairly well with the experimental shadowgraph images. In contrast, the results of URANS distinctly disagree with those of the ZDES case and the experiments.