An Improved Numerical Method for Unsteady Lifting Surfaces in Incompressible Flow

Abstract

Usable range of reduced frequency are investigated for some of representative unsteady numerical lifting surface theories. They are three current methods and one new method developed in this paper. The former three methods, containing two doublet lattice methods and DAVIES' method, reveal their own defects.
The proposed method consists of asymptotic expansion of the kernel function and appropriate treatment of the singularities. A whole lifting surface is divided into many chordwise strips, through a spanwise Semi-Circle-Method (SCM). A special care is taken for the "singular strip" in which the control point is contained. It is found that the present method improves remarkably defects of the above three methods.