A high-fidelity numerical database for free-stream-turbulence-induced transition under varying pressure gradients

Abstract

Free-stream-turbulence-induced transition under streamwise-varying pressure gradients, as encountered on turbine blades, has received much less attention in high-fidelity simulations than its zero-pressure-gradient counterpart. The ERCOFTAC T3 experiments provide a carefully documented reference for this problem and remain central to transition-model calibration. Complementing them with full-field, three-dimensional data opens new opportunities for the development of physics-based and machine-learning transition models. To this end, wall-resolved implicit large-eddy simulations of the T3A, T3B, and T3C2--C5 flat-plate cases are performed with a high-order compressible solver, using an upstream slip-wall block that lets the synthetic free-stream turbulence develop up to the leading edge. The simulations reproduce well the measured transition locations, integral quantities, and velocity profiles, and predict a separation bubble near the end of the plate for the lowest-Reynolds-number case T3C4. As the Reynolds number decreases and transition moves into the adverse-pressure-gradient region, the mechanism evolves continuously from classical bypass transition to transition governed by the tendency of the laminar boundary layer to separate, up to separation-induced transition. Intermittency, conditioned statistics, and Reynolds-stress budgets document this evolution and the associated non-equilibrium effects, which challenge current RANS transition models.

arXiv commentThe high-fidelity numerical database associated with this work is publicly available on Zenodo: https://doi.org/10.5281/zenodo.17166216