Abstract: An improved algorithm for velocity field of general configurations is presented for low-order panel method based oD the internal Dirichlet boundary condition,A direct calculating method for the velocity distribution by means of a limit process combining with analytic evaluation of high-order singular integrals instead of the conventional method of doublet strength gradient is devised in order to avoid the difficulty of edge extrapolation of doublet strength.The problem that the in-duced drag coefficient obtained from the VSAERO analysis is substantially underpredicted has dis-appeared for the present improved algorithm. Illustrative calculations for several test cases such as swept back wing,swept forward wing and wing-body combination show that the accuracy of re-sults may be improved and is competitive with high-order panel method.In addition,the present direct integral method can be used to evaluate the velocity distribution for external flow field cor-rectly where the method of gradient cannot be used at all.

Key words: panel method (fluid dynamics), Dirichlet problem, velocity distribution