The Effects of Nonlinearly on the Unsteady Force of Two-Dimensional Airfoils

Abstract

The effects of nonlinearity on unsteady force in two-dimensional potential flow are studied. The nonlinearities of airfoil thickness, camber and angle of attack have the effect to retarding the build-up of lift, whereas the wake-deformation has an opposite effect. The thickness and camber also have the effect of increasing the force of apparent mass which is proportional to the acceleration of the flow. The general formula to obtain the initial lift and drag of impulsively started airfoils of arbitrary-shape is derived and in the case of Joukowski airfoils, the solution is compared with Chow and Huang's approximate solution, which is valid when the camber is slight and angle of attack is small.