Effects of Ultra-High Reynolds Number and Low Mach Number Compressibility on the Static Stall Behavior of a Wind Turbine Airfoil

The increasing scale of wind turbines introduces significant aerodynamic challenges at ultra-high Reynolds numbers and under conditions of low Mach number compressibility. The stall behavior, flow separation, and boundary layer transition are all significantly changed by these characteristics. However, wind tunnel testing cannot concurrently satisfy Re-Ma similarity, and current design frameworks ignore their associated impacts, leading to a great deal of uncertainty in load prediction and power efficiency for next-generation turbines. To bridge this gap, we utilize high-fidelity CFD simulations combined with parametric scaling to develop a novel size-based decoupling technique. With Re and Ma independently controlled by changing chord length and freestream velocity, the FFA-W3-211 airfoil is used as the benchmark. Static stall prediction accuracy is confirmed by validations against the wind-tunnel experimental data of S809 and VR-7B airfoils. The results show that the influence of a high Reynolds number markedly postpones flow separation and enhances pressure distribution, delaying the onset of stall. In contrast, the effect of a high Mach number hastens flow separation and deteriorates pressure distribution due to shock-induced separation, leading to an earlier occurrence of stall. For angles of attack lower than 12°, the influence of the Reynolds number prevails, effectively counteracting the negative impacts of the Mach number. For angles of attack greater than 12°, the two effects combine to raise the risk of flow instability considerably. This study focuses on independently analyzing the effects of the Reynolds and Mach numbers on the stall behaviors of wind turbine airfoils.