Numerical and Experimental Study of Airfoils with Porous Trailing Edge

Abstract

The addition of porous material to the trailing edge of airfoils was studied numerically and experimentally. The purpose of this work is to inspect whether the penalization method can be successfully used to describe flows through porous media. In the numerical study, the penalization method was applied to the incompressible Navier-Stokes equations. The flow has been studied with turbulent, unsteady simulations. The SIMPLE algorithm and a mixed scale model for LES were used in EllipSys2D. The code was validated with a test case on a flat plate. In this case, porous inserts are capable of suppressing vortex shedding by mitigating the pressure discontinuity at the trailing edge. An agreement with wind tunnel data could be observed both in the wake and in the boundary layer. The code was then applied to study a NACA0018 airfoil at zero angle of attack. In this case, porous materials reduce the energy content of turbulent signals in the wake. The power spectral density of pressure fluctuations in correspondence of the porous insert is reduced in the whole spectrum. The same airfoil was considered with the addition a single roughness element to trip the boundary layer at 20% of the chord. The height of the step was chosen from the results of a sensitivity analysis. The presence of the trip triggers turbulence transition successfully. Pressure drag for the porous case was found to be dependent on the presence of the trip. In the experimental study, measurements were taken on a symmetric NACA0018 airfoil at zero angle of attack. Hot-wire anemometry and surface microphones were used to measure the flow. Porous inserts with different permeabilities have been studied. Porous materials at the trailing edge increase the shear of velocity profiles in the boundary layer and reduce the power spectral density of pressure fluctuations in correspondence of the trailing edge. According to this study, the penalization method is a promising tool to study flows through porous media.