Assessment of the Sonic-Eddy Model in Hypersonic Turbulent Boundary Layers

Abstract

Hypersonic turbulent boundary layers exhibit strong compressibility and acoustic effects that alterturbulent momentum transport and complicate the interpretation of near-wall structure. A central unresolved question is how finite acoustic signaling speed limits the size, coherence, and effectiveness of the eddies responsible for transferring momentum across the boundary layer. This thesis evaluates the sonic-eddy transport model, in which turbulent transport is constrained by eddies for which the acoustic communication time across the eddy is comparable to or shorter than the eddy turnover time. Under this framework, the outer region of the boundary layer acts as a bottleneck for momentum transfer from the freestream to the wall, leading to specific predictions for eddy-size variation and skin-friction scaling with Mach number. Three-dimensional viscoussublayer-resolved Reynolds-stress-model computations of hypersonic turbulent boundary layers were used to examine these predictions and to assess the extent to which the sonic-eddy model is consistent with the computed mean flow behavior. The results are broadly consistent with the key predictions of the sonic-eddy transport model and provide insight into its validity and limitations for hypersonic wall-bounded turbulence.