Simulation of Small Scales in a Temporally Evolving Compressible Turbulent Mixing Layer Using the Two-Level Simulation Model

In this study, we present results from examining the capabilities of the two-level simulation (TLS) model to simulate small scales in a temporally evolving compressible turbulent mixing layer. TLS is a multi-scale modeling strategy, where both large- and small-scales of motion are explicitly simulated in a coupled manner. It utilizes a scale decomposition strategy to segregate a flow variable into the large-scale (LS) and small-scale (SS) flow variables and to obtain the corresponding governing equations. The explicit simulation of the SS flow field leads to the unique capabilities of the TLS model compared to a large-eddy simulation strategy, where the effects of unresolved small scales of motion on the resolved large scales of motion are modeled. We assess the capabilities of the model, particularly, focusing on the evolution of the SS flow field in a temporally evolving non-reacting compressible mixing layer comprising streams of O2 and N2 at a convective Mach number of 1.1 and vorticity-thickness-based Reynolds number of 640. The assessment is performed during the early stages of the self-similar state of the mixing layer, which is marked by complex physical processes that are difficult to model. First, results from direct numerical simulation are discussed to show that the data can be considered for the assessment of the TLS model. Afterward, results from a priori and a posteriori assessment of the SS flow fields are discussed. The results show that the modeling assumptions employed to simplify the SS governing equations by the TLS model tend to be adequate and the modeled SS flow field can reasonably capture the spectral and spatial characteristics of the SS flow field.