Knowledge on the boundary-layer transition location at large chord Reynolds numbers is essential to evaluate the performance of airfoils designed for modern wind-turbine rotor blades. In the present work, a temperature-sensitive paint was used to systematically study boundary-layer transition on the suction side of a DU 91-W2-250 airfoil. The experiments were performed in the High-Pressure Wind Tunnel Göttingen at chord Reynolds numbers up to 12 million and angles of attack from $-14$ to 20°. The coefficients of airfoil lift, drag, and pitching moment were also obtained after integration of the pressure distributions measured on the surface and in the wake of the wind-tunnel model. The global information obtained via temperature-sensitive paint not only enabled the analysis of the change in the transition location with varying angle of attack and chord Reynolds number, but also provided an explanation for the evolution of the aerodynamic coefficients measured at stall and poststall conditions. The stability of the laminar boundary layers investigated in the experiments was analyzed according to linear stability theory. The results of the stability computations supported the experimentally observed variations in the transition location. The amplification factors of boundary-layer disturbances at transition were also determined by correlating the experimental and numerical results.

大弦雷诺数下边界层过渡位置的知识对于评估为现代风力涡轮机转子叶片设计的翼型的性能至关重要。在目前的工作中，一种温度敏感涂料被用于系统地研究 DU 91-W2-250 翼型吸力侧的边界层转变。实验在高压风洞哥廷根进行，弦雷诺数高达 1200 万，攻角为$-14$到 20°。翼型升力、阻力和俯仰力矩的系数也是在对表面和风洞模型后测得的压力分布进行积分后获得的。通过温度敏感涂料获得的全局信息不仅可以分析随着迎角和弦雷诺数变化的过渡位置的变化，而且还为失速和失速条件下测量的空气动力学系数的演变提供了解释。根据线性稳定性理论分析了实验中研究的层流边界层的稳定性。稳定性计算的结果支持实验观察到的过渡位置变化。