Influence of Steady Pitch Rate on 2-D Airfoil Aerodynamic Characteristics at Incidence

Abstract

I N various dynamic problems it is important to know the constituent parts of aerodynamic loads due to pitch rotation. However, the attention given to this question at higher angles of attack with flow separation has been very low. Sometimes the problem of modeling aerodynamic loads due to steady pitch rotation is mixed up with modeling aerodynamic loads due to incidence variation. Some discussions of the question can be found in [1]. These are really two distinct tasks. The first task is a steady one. It is possible to imagine motions with a constant angle of attack and various pitch rates. These are circular orbital motions with various radii. On the other hand a translational motion with zero pitch rate and varying incidence could exist also. In the first case the circulation is constant. In the second case a time-dependent vortex wake exists behind the body. The present work is devoted to some estimations using thin airfoil theory of pitch rate effects on a 2-D airfoil with flow separation at high constant angles of attack. For low angles of attack the influence of steady pitch rate on airfoil loads was investigated, for example, in [2]. For the case of zero pitch rate the effects of flow separation on aerodynamic loads was investigated using the linearized thin airfoil theory in [3]. This approach was now applied to estimations of pitch rate effects on a 2D airfoil with flow separation at high constant angles of attack. For comparison, numerical estimations from the well-known XFOIL code [4] were used. The effect of steady pitch rate is simulated using the approximate technique of curved models [5] (pitch rate induced curvature).