Transition prediction for high-lift flows using a crossflow-extended RANS transition model with overset grid

High-lift flow simulations remain challenging for Reynolds-averaged Navier–Stokes methods, largely due to the coexistence of laminar separation bubbles, boundary-layer transition, wake/shear-layer interactions, and three-dimensional effects. In this work, boundary-layer transition for complex high-lift configurations is investigated using the correlation-based γ–Reθt framework implemented in the NASA CFL3D solver on overset grids. To extend applicability to swept-wing configurations, a localized crossflow-transition treatment is incorporated by augmenting the intermittency equation with a crossflow-induced production mechanism. The study is organized as a sequence of capability-building steps. First, a transonic transport configuration (CHN-T1 BWHV) is used to establish an overset-grid construction strategy and conduct a grid-convergence assessment as a baseline. Then, transition-model capability is validated using cases comprising two-dimensional and three-dimensional transition mechanisms, including a zero-pressure-gradient flat plate, the NLR-7301 two-element airfoil for overset-grid/transition behavior, and the NLF(2)-0415 infinite-span swept wing, to assess the crossflow extension. Finally, two high-lift configurations (MDA 30P/30N and the NASA trapezoidal wing) are investigated as application cases. Overall, the results show that overset-grid-based simulations provide a practical approach for investigating transition behavior in high-lift configurations, while the main findings lie in the assessed transition-model behavior and the effect of the crossflow extension. For swept-wing/high-lift configurations where crossflow instability is significant, the crossflow extension shifts the predicted transition onset upstream in crossflow-sensitive regions and improves agreement with reference transition trends. Remaining discrepancies are mainly associated with complex wake–boundary-layer mixing and three-dimensional effects, especially in flap regions, indicating the need for further robustness improvement in strongly coupled separated or interaction-dominated flows.