Effect of Gurney flap on flow separation and aerodynamic performance of an airfoil under rain and icing conditions

In the present study, special attention is paid to numerically investigate the aerodynamic performance of the NACA 0012 airfoil under rain and icing conditions with the aim to better understand the severe aerodynamic performance penalties of aircraft in flight. Furthermore, in order to control the flow separation and improve the aerodynamic performance of the airfoil under critical atmospheric conditions, the Gurney flap with different heights is attached to the trailing edge of the airfoil. The simulation is done at a Reynolds number of 3.1 × 10⁵ under different atmospheric conditions including dry, rain, icing and coupling of rain and icing conditions. A two-way momentum coupled Eulerian–Lagrangian multiphase method is used to simulate the process of water film layer formed on the airfoil surface due to rainfall. According to the results, accumulation of water due to rainfall and ice accretion on the airfoil surface inevitably provides notable negative effects on the aerodynamic performance of the airfoil. It is concluded that icing induces a higher aerodynamic degradation than rain due to very intensive ice accretion. The Gurney flap as a passive flow control method with a favorable height for each condition is very beneficial. The maximum increment of the lift-to-drag ratio is achieved by Gurney flap with a height of 0.01 of airfoil chord length for dry and rain conditions and 0.02 of airfoil chord length for icing and coupling of rain and icing conditions, respectively.