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Abstract

Accurate prediction of laminar-to-turbulent transition is crucial for analyzing the aerodynamic performance of airfoils in moderate Reynolds number applications, such as wind turbine blades and unmanned aerial vehicles. While the Reynolds-Averaged Navier-Stokes (RANS) framework with eddy viscosity models remains a widely used approach due to its computational efficiency, its capability to predict transition accurately often falls short compared to high-fidelity methods such as Direct Numerical Simulation (DNS) and Large Eddy Simulation (LES). This limitation is particularly pronounced in moderate Reynolds number flows, where transition phenomena are highly sensitive to flow conditions and model parameters. This study focuses on modifying specific parameters within the 𝛾-SST transition model to enhance its predictive accuracy for moderate Reynolds number flows. In this work, key parameters such as the transition onset criteria and intermittency production terms are systematically adjusted. A Monte Carlo targeting method is employed to explore the parameter space and identify optimal combinations that minimize discrepancies with high-fidelity data. The improved model is then rigorously validated by simulating transitional flows over NACA0018 airfoils, where transition occurs by different mechanisms on each airfoil. Although the improved model exhibits enhanced predictive performance for key transition characteristics relative to the original model, such as transition onset location, boundary layer growth, pressure distribution, and friction distribution, its inherent reliance on empirical correlations developed primarily for separation-induced transition mechanisms limits its accuracy when predicting natural transition. Specifically, the model tends to predict the separation phenomena in cases where a natural transition occurs erroneously. However, the improved model still demonstrates a more accurate overall performance compared to the baseline model. This work establishes a refined transition modeling approach that, despite its limitations, balances computational efficiency and predictive accuracy, offering a practical approach for engineering analysis of airfoil aerodynamics in moderate Reynolds number regimes. The findings highlight that further advances aimed at predicting laminar-to-turbulent transitions within the RANS framework must incorporate additional flow physics, such as receptivity to free-stream disturbances.