Since the high-altitude long-endurance unmanned aerial vehicles operate in the challenging low-Reynolds-number regime, it is critical to accurately predict the flow separation and transition for airfoil design. This study assesses the prediction accuracy of the widely used γ–R̃eθt two-equation transition model and subsequently presents comprehensive calibrations of its embedded empirical correlations using wind tunnel experimental data of the E387 airfoil. Modified correlations are developed through systematic parameter optimization of the transition onset length function Flength and the critical momentum-thickness Reynolds number Reθc. Computational results for a series of test cases demonstrate that the modified empirical correlations significantly reduce the relative error in the predicted lift-to-drag ratio of the airfoil when comparing against the experimental data across a Reynolds number range of 1.0×105–3.0×105. In contrast, predictions using the original model and the Tomac correlations exhibit errors exceeding 10% for most test cases. Moreover, additional typical low-Reynolds-number airfoils are selected to further validate the improved prediction accuracy of the modified model. The results at Re≈6×104 indicate that the proposed calibration method is effective.
Xu et al. (Wed,) studied this question.