Influence of separation structure on the dynamics of shock/turbulent-boundary-layer interactions

Abstract

Shock/turbulent-boundary-layer interactions (STBLIs) are ubiquitous in high-speed flight and propulsion applications. Experimental and computational investigations of swept, three-dimensional (3-D) interactions, which exhibit quasi-conical mean-flow symmetry in the limit of infinite span, have demonstrated key differences in unsteadiness from their analogous, two-dimensional (2-D), spanwise-homogeneous counterparts. For swept interactions, represented by the swept–fin-on-plate and swept–compression–ramp-on-plate configurations, differences associated with the separated shear layers may be traced to the intermixing of 2-D (spanwise independent) and 3-D (spanwise dependent) scaling laws for the separated mean flow. This results in a broader spectrum of unsteadiness that includes relatively lower frequencies associated with the separated shear layers in 3-D interactions. However, lower frequency ranges associated with the global “breathing” of strongly separated 2-D interactions are significantly less prominent in these simple, swept 3-D interactions. A logical extension of 3-D interaction complexity is the compound interaction formed by the merging of two simple interactions. The first objective of this work is therefore to analyze the more complex picture of the dynamics of such interactions, by considering as an exemplar, wall-resolved simulations of the double-fin-on-plate configuration. We show that in the region of interaction merging, new flow scales, changes in separation topology, and the emergence of lower-frequency phenomena are observed, whereas the dynamics of the interaction near the fin leading edges are similar to those of the simple, swept interactions. The second objective is to evolve a unified understanding of the dynamics of STBLIs associated with complex configurations relevant to actual propulsion systems, which involve the coupling between multiple shock systems and multiple flow separation and attachment events. For this, we revisit the salient aspects of scaling phenomena in a manner that aids in assimilating the double-fin flow with simpler swept interactions. The emphasis is on the influence of the underlying structure of the separated flow on the dynamics. The distinct features of the compound interactions manifest in a centerline symmetry pattern that replaces the quasi-conical symmetry of simple interactions. The primary separation displays topological closure to reveal new length scales, associated unsteadiness bands, and secondary flow separation.

Dynamics of Three-Dimensional Shock-Wave/Boundary-Layer Interactions

“…In this interaction, the behavior near each fin exhibits quasi-conical properties, but new features, including a pair of streamwise-oriented vortices, arise in the central interaction region (Schmisseur & Gaitonde 2001). A particularly interesting aspect of the dynamics is the appearance of a band of lower-frequency unsteadiness that is reminiscent of the separation of frequency scales found in 2D SBLI, while not necessarily reflective of the same underlying mechanisms; this is discussed in detail by Adler & Gaitonde (2022). For these interactions, the dependence of nonasymptotic behavior on Mach and Reynolds numbers has not been adequately characterized; these parameters may strongly affect the scaling considerations between ground and flight tests, as well as correspondences between the former and high-fidelity simulations that tend to consider lower Reynolds numbers for computational feasibility.…”

“…The DF SBLI, which is of increasing interest in hypersonic applications, may be viewed as a compound interaction, resulting from the merger of the two quasi-conical interactions, each generated by one of the opposing fins. Recent efforts (Adler & Gaitonde 2022, Seckin et al 2022 have contributed newer techniques to the classical literature (Zheltovodov 2006, Gaitonde 2015. In this interaction, the behavior near each fin exhibits quasi-conical properties, but new features, including a pair of streamwise-oriented vortices, arise in the central interaction region (Schmisseur & Gaitonde 2001).…”

Special issue on the fluid mechanics of hypersonic flight

“…Solution of the adjoint problem has also been used to compute the wavemaker and propose the physical mechanism of the observed instability scenario. Three-dimensional turbulent separation effects are at the core of the work of Adler and Gaitonde [2], who address the issue of separation arising from shock/boundary layer interactions in three-dimensional configurations of increasing geometric complexity. Using a very large database of experimental and simulation results, these authors catalog unsteady phenomena on the basis of frequency bands and describe qualitative differences between two-dimensional, axisymmetric, open three-dimensional separation in the absence of sidewalls, as well as the effect of the latter on the proposed characterization.…”

On wall pressure fluctuations in conical shock wave/turbulent boundary layer interaction

“…Abe (2017) continued research of Na & Moin (1998) based on DNS at different Reynolds number (), finding that the scaling law of exhibits good agreement in the APG region with the data of Na & Moin (1998), at low frequencies. Recently, Adler & Gaitonde (2020, 2022) carried out an LES study to investigate the unsteadiness in three-dimensional (3-D) sharp-fin and swept-compression-ramp interactions. They found that flow separation in 3-D interactions is topologically different than two-dimensional (2-D) SBLIs.…”