Improved γ-Re_θ transition model for hypersonic cavity-induced transition predictions

Surface irregularities such as local cavities can disturb the boundary layer flow, resulting in local peaks of aerodynamic heating. If the boundary layer flow enters the interior of a local surface cavity, the laminar-to-turbulent transition may be enhanced. In this work, an improved γ-Re_θ transition model for predicting cavity-induced transition is developed. Analysis of the flow structures around the cavity indicates that flow separation occurs in the cavity and a strong adverse pressure gradient appears near the trailing edge. The pressure gradient parameter λ_ζ is proposed as an indicator for local susceptibility to the separation instability. The separation intermittency γ_sep,new, which is constructed based on λ_ζ, is used to account for the effect of separation on the transition. The improved transition model is validated by observing the Mach 6 flow across cavities installed on a flat plate and the windward surface of the Shuttle Orbiter configuration. In addition, the Hypersonic Inflatable Aerodynamic Decelerator configuration is used to further substantiate its universality and appropriateness in separated-flow transition around such a complex configuration. The numerical results show that the improved γ-Re_θ transition model simulates the augmentation of heating and the cavity-induced transition from laminar to turbulent flow, and is in reasonable agreement with experimental results.