Aircraft often operate in humid atmospheres, where water-vapor phase changes can alter the flow structure. Although buffeting is observed around airfoils under certain operating conditions in the transonic regime, the effects of humidity on this phenomenon remain insufficiently understood. In this study, numerical simulations were conducted to clarify the effects of atmospheric humidity on transonic buffet over an airfoil. A delayed detached-eddy simulation was applied to the transonic flow around an OAT15A supercritical airfoil, which exhibited a typical buffet phenomenon in the experiment. The governing equations were coupled with a nonequilibrium condensation model that included homogeneous nucleation and droplet growth. The free-stream relative humidity (RH) was varied from 0% to 100%. Under the dry condition, a typical transonic buffet is reproduced, consistent with the experimental observations. As the humidity increases, the latent heat release in the supersonic region ahead of the main shock reduces the effective Mach number, weakens the main shock, and shifts it downstream. At an intermediate humidity (approximately 60% RH), the flow becomes quasi-steady: a condensation shock forms upstream, and a lambda-shaped stepped compression appears, which eases the shock/boundary-layer interaction and strongly suppresses the large-amplitude buffet. At a higher humidity, a self-sustained unsteadiness develops, characterized by moving shocks that detach from the main shock and propagate toward the leading edge. This resulted in oscillations with a higher dominant frequency than in dry air. Dynamic mode decomposition shows that the suction-side feedback mechanisms differ between dry and high-humidity conditions. Moreover, aerodynamic performance varied nonmonotonically with humidity.
Takuma et al. (Sun,) studied this question.