Transition Model for Second Mode and Crossflow Instabilities in Hypersonic Flow

A novel unified transition model for high-speed boundary-layer flows is presented. The model integrates amplification factor transport equations for second mode and crossflow instabilities. The transport equation source terms are modeled with neural networks and the formulation is Galilean invariant. The neural networks are trained with extensive databases obtained from linear stability theory analyses for a wide and diverse set of compressible boundary layers that covers different Mach numbers, wall temperature ratios, pressure gradients, and Reynolds numbers as well as different radii and cone half angles for axisymmetric boundary layer flows and sweep angles for three-dimensional boundary layer flows. A grid convergence study is carried out for a Mach 6 boundary layer over a flat-plate. The model is then employed for predicting transition of Mach 6 boundary layer flows over a two-dimensional flared wedge, a circular cone at zero angle of attack, and the HIFiRE-5 configuration. Four all four cases, the amplification factor prediction is in good agreement with linear stability theory.