Investigating suggested airfoil geometries at air velocities that are within the natural wind speeds

Abstract

Many “suggested” airfoil geometries, that have the same chord length, are investigated. Each geometry is checked at two attack angel values, α, that equal 0° and 30°, and at values of Reynolds number, Re, that equal 822000, 1232300, 1643000, 2054000, and 2465000. The results of the lift and drag coefficients, C_L and CD, are compared with those of the standard airfoil N6409. The airfoil geometry which consists mainly of two intersecting circular arcs exhibited relatively higher C_L values. The performance of this airfoil was found to be considerably affected by the two non-dimensional radii of curvature, ${\hat{R}}_1$ and ${\hat{R}}_2$. So, fifteen cases of this promising geometry were tested with different values of, ${\hat{R}}_1$ and ${\hat{R}}_2$ and with the different values of Re mentioned above. The results showed that, although the C_L values were higher than those of the N6409 airfoil, but the C_D values were large too. The case whose, ${\hat{R}}_1$ and ${\hat{R}}_2$ equal 0.56 and 0.83 respectively, exhibited the highest C_L values for all Re and α values. To validate the results of this geometry, it was tested experimentally and numerically at α = 0, 5, 10, 15, 20, 30, and both the numerical and experimental results were in an acceptable agreement. This geometry is suitable for the wind turbine applications. Four correlations were suggested to relate the C_L and C_D to Re, ${\hat{R}}_1$ and ${\hat{R}}_2$ for α = 0° and α = 30°. When testing these correlations, the maximum deviations of the calculated C_L and C_D values from those of the numerical and experimental results were within the range from 9 to 13%.