Transonic flow of moist air around a thin airfoil with equilibrium condensation

The two-dimensional and steady transonic flow of atmospheric moist air with equilibrium condensation around a thin airfoil is investigated. The study is based on an asymptotic analysis and numerical simulations. A small-disturbance model is developed to explore the nonlinear interactions between the near-sonic speed of the flow, the small thickness ratio and angle of attack of the airfoil, and the small amount of mass of water vapor in the air. The condensation process of water vapor in the air is assumed to be isentropic. The similarity parameters that govern the flow problem are provided. The flowfield may be described by a modified transonic small-disturbance (TSD) equation that includes parameters that are related to the condensation process. Murman and Cole's method (Murman, E. M., and Cole, J. D., "Calculation of Plane Study Transonic Flows," AIAA Journal, Vol. 9, No. 1, 1971, pp. 114-121.) is used for the numerical solution of the modified TSD problem. The results show that the flow of moist air is similar to the flow of dry air with an effective freestream Mach number that is greater than the freestream Mach number of moist air. The present approach is used to study the aerodynamic performances of airfoils in atmospheric transonic flight with humidity.