Numerical validation of the squire-young formula for profile-drag prediction

The Squire-Young formula is widely used to calculate profile drag in two-dimensional airfoil analyses. Although experience shows that the formula provides reasonable and accurate predictions, full Navier-Stokes computational fluid dynamics allows for a numerical validation of the formula. A method is presented for evaluating the Squire-Young formula from a computational fluid dynamics solution, and demonstrated for several airfoils. The agreement between profile-drag coefficients determined using the Squire-Young formula and those calculated directly from the computational fluid dynamics solution using surface integration is typically within 2-3% in the low-drag range, with error increasing at higher lift coefficients. The applicability of the underlying assumptions is discussed, and the validityof the assumed variationof shape factor and edge velocity in the wakeis investigated for asymmetric airfoil at zero lift. The formula is also demonstrated as being insensitive to spurious drag that may occur due to far-field boundary conditions. Finally, a derivation of the Squire-Young formula is included to further aid in understanding the influence of its assumptions on its predictions.