Numerical value analysis on aerodynamic performance of DU series airfoils with thickened trailing edge

Abstract: In order to analyze the aerodynamic performance of blunt trailing edge airfoils with different thicknesses of trailing edge and maximum thicknesses to chord, in this paper, a method called blending function of exponential was used to enlarge the trailing edge of airfoil. The aerodynamic performance of blunt trailing edge airfoils generated from the DU91-W2-250, DU97-W-300 and DU96-W-350 airfoils by enlarging the thickness of trailing edge symmetrically from the location of maximum thickness to the chord to the trailing edge to 5%c and 10%c were analyzed by using CFD method at a chord Reynolds number of 3×106. c denotes the length of the chord line. The calculation domain is a circular domain with a radius of 50c. The airfoil surface was set as an adiabatic no-slip wall boundary condition. A velocity-inlet boundary condition was applied at the inflow boundary and the pressure-outlet boundary condition was applied at the outflow boundary. The transition SST model can accurately predict the aerodynamic performance of conventional and blunt trailing edge airfoils with clean surfaces. The results calculated by the SST turbulence model can represent the aerodynamic performance of airfoils with rough surfaces. The steady calculated results show that the lift of clean airfoil can be predicted accurately by two dimensional CFD calculation while the drag of blunt trailing edge airfoils with larger trailing edge thickness cannot be calculated precisely even at low angles of attack. The aerodynamic performance of blunt trailing edge airfoils with larger trailing edge thickness should be predicted by more accurate three dimensional CFD method further. With the increase of the thickness of trailing edge, the increase rate and amount of lift becomes limited gradually at low angles of attack, while the drag increases dramatically. The larger the thickness of the trailing edge is, the higher the maximum lift is, but too large lift can cause abrupt stall. So the thickness of the trailing edge should be constrained in a certain rage. For example, 5%c is a better choice for blunt trailing edge airfoils, the lift of these airfoils has been increased but with no abrupt stall. In this paper, pressure distributions on original airfoils and trailing edge enlarged airfoils under ten degrees angles of attack calculated by both fully turbulent k-ω SST model and transition k-ω SST model were analyzed. On the one hand, by enlarging the trailing edge of the airfoil symmetrically, the adverse pressure gradient near trailing edge on suction side can be reduced, the reduced pressure gradient can suppress the reduction of flow velocity in boundary layer due to viscosity and the separation of boundary layer can be delayed consequently. On the other hand, the pressure differential between the pressure side and suction side can be increased. The increase of thicker airfoil's pressure differential is larger than other thinner airfoils. Besides, the increase amount of lift of trailing edge enlarged airfoils calculated by fully turbulent model is larger than that calculated by free transition turbulence model. Compared with free transition condition, the fully turbulent boundary layer are more sensitive to the enlargement of trailing edge thickness.