Aerodynamics of Airfoils Subject to Three-Dimensional Periodic Gusts.
Abstract
A general analysis of periodic three-dimensional vortical disturbances of streaming motions around streamlined and bluff bodies is developed using a unified approach wherein the mathematical problem is reduced to solving a single inhomogeneous wave equation with non-constant coefficients. In the limit of vanishing Mach number, the problem is formulated in terms of an inhomogeneous Fredholm integral equation of the second kind. The analysis is first applied to study the unsteady aerodynamics of an airfoil of arbitrary shape moving at low Mach umber in a three-dimensional periodic gust pattern. Because the homogeneous equation has a non-trivial solution, a special procedure was developed for its solution and uniqueness is obtained by applying the Kutta condition at the trailing edge. Results were compared with those obtained from a nonlinear two dimensional gust theory and linear oblique gust analyses. Comparison shows a very strong influence of the airfoil geometry and mean flow angle of attack and of the gust parameters on the unsteady lift and moment coefficients. In fact, depending on the conditions considered, the unsteady lift and moment coefficients can be several times larger or smaller than those obtained from linear theories. A superposition principal was derived whereby the unsteady lift and moment acting on a thin airfoil with small camber and small angle of attack and subject to a two-dimensional gust can be constructed by linear superposition to the Sears lift and moment of three independent components accounting separately for the effects of airfoil thickness, airfoil camber and non-zero angle of attack of the mean flow.
Document Details
- Document Type
- Technical Report
- Publication Date
- Aug 31, 1983
- Accession Number
- ADA145149
Entities
People
- H. Atassi
Organizations
- University of Notre Dame