Computational fluid dynamics simulation of aerodynamic performance and flow separation by single element and slatted airfoils under rainfall conditions

Abstract

This study investigated the effects of rainfall on flow separation and the aerodynamic performance of single element and slatted NACA 0012 airfoils by using a mathematical model developed with the commercial computational fluid dynamics solver ANSYS FLUENT 18.2. A two-way momentum coupled Eulerian–Lagrangian multiphase approach was used to simulate the formation of the water film layer on the airfoil's surface. According to the results, very low values of the lift-to-drag ratio at low angles of attack reflected severe degradation of the aerodynamic performance of the airfoil in the presence of water accumulated on its surface. The impact of rain droplets on the leading-edge slat surface led to less water accumulating on the main section of the airfoil. In particular, the maximum water film mass concentrated on the airfoil surface decreased from 15 g to 1 g compared with the single element airfoil. Hence, the thickness of the water film layer was not sufficiently large to significantly affect the aerodynamic coefficients of the slatted airfoil, especially the maximum lift coefficient, compared with the thicker water film layer on the single element airfoil. In addition, the use of slats clearly enhanced the aerodynamic coefficients and increased the stall angle from 13° to 22° in dry conditions, and from 16° to 24° in rainy conditions. Slats also significantly decreased the boundary layer thickness and delayed the separation at higher angles of attack.