Numerical Analysis of NACA 6409 and Eppler 423 Airfoils

Abstract

The present study aims to numerically examine two commonly used airfoils that provide high lift at low Reynolds numbers, using various turbulence models with the commercial code ANSYS Fluent 19. Eppler 423 airfoil is widely used in wind turbine blades, wings of gliders and R/C airplanes designed for sport flying and competitions thanks to high lift capability. NACA 6409 airfoil is seen in free-flight model planes. In literature review, it has been found that k-ω SST, k-kl-ω and 𝛾-𝑅𝑒𝜃 transition models have a good prediction in Cl-Cd estimation of drag bucket region, transition flow regime, and laminar separation point. In addition to RANS models, laminar model was also investigated. In order to ensure the accuracy and precision of numerical investigations; the grid sensitivity study and near wall model were used. The method of decomposition of flow direction vector procedure has been used to provide the advantage of simulating all angle of attacks using only a single mesh. The lift coefficient curves and polar diagrams were formed from the angle of attack of -4 degree up to the stall. Experimental data, XFoil analysis data and numerical analysis data were evaluated in terms of best glide ratio-(Cl/Cd)max and minimum sink-(Cl1.5/Cd)max criteria. As expected, at high angle of attack, the transition ramp on the upper surface moves forward and the pressure gradient became more adverse. The results showed that fine mesh gives better results than other mesh sizes and transitional γ-Reθ SST model was successful in modelling the transition event than other turbulence models.