Evaluation of the SST-γ and SST-γ-νL models for transition in high-speed boundary layers

The prediction of laminar-turbulent transition is a critical aspect of design for hypersonic flight systems, but this need is currently not met by the transition models available in production CFD codes. Many extensions to existing low-speed models as well as new transition models have been suggested to address this technology gap. However, in order to have the necessary understanding and trust in these models to be used in design settings, an extensive verification and validation effort is required. The present work is a part of the effort to validate these models and to develop deeper understanding of their characteristics and their domain of applicability. To that end, two recently-developed models, a model within the SST-$\gamma$ framework and a model based on SST-$\gamma -{\nu }_L$ equations, have been implemented in NASA’s OVERFLOW 2.3e solver. In this paper, these models are applied to a suite of test cases that they have not previously been used for. This guarantees that none of the test cases investigated were part of the set of cases used to calibrate the models and enables an analysis of a wider set of Mach number and free-stream disturbance characteristics than has previously been carried out for these models. The assessment demonstrates that the SST-$\gamma$ framework is computationally robust, but predicts increasingly inaccurate transition zone characteristics at higher Mach numbers. Although the SST-$\gamma -{\nu }_L$ framework is shown to be numerically stiff, it consistently offers reasonable predictions for the test cases examined herein with freestream Mach numbers less than 14. The performance of both models can be enhanced in several ways, which are described.