A numerical simulation on the airfoil S833 equipped with flapping trailing edge fringes

Abstract

Design optimization has been increasingly investigated for an airfoil, aiming to reduce the vorticity in the wake and increase the aerodynamic performance. In the current work, a two-dimensional (2D) S833 airfoil equipped with a flapping fringe at the trailing edge has been studied using computational fluid dynamics (CFD) simulations. The objective is to investigate the influence of the length (Lf) and flapping frequency (f) of the fringe on shedding vortices from the airfoil and the drag and lift coefficients. The validation of the current numerical approach for both static and dynamic motions of the airfoil was conducted. First, four different computational meshes were created for the static bare airfoil S833 model, and the simulated drag and lift coefficients were compared against experimental results. It is observed that the second finest mesh contributes to the best agreement with the measurement data. In addition, the numerical accuracy of the dynamic simulation was assessed by reproducing the pressure distribution around the airfoil NACA0014 with a periodic plunging motion at different time phases within one plunging cycle. Good agreements between the simulated and previous computational results are obtained. Moreover, the investigation of S833 airfoil equipped with a flapping fringe reveals that the model with Lf =0.01 m (10% of the chord length) associated with a flapping frequency below the shedding frequency of the bare airfoil can significantly alter the coherent structure of the shedding vortices, breaking the routine large-scale vortex into small-scale weak vortices. It also results in reducing the intensity of vortices and shortening the distance between each pair of vortices to accelerate the dissipation of vorticity. In addition, the equipped flapping trailing edge fringe can achieve extra benefit in aerodynamic performance in terms of the reduction of the drag coefficients and the enhancement of lift coefficients.