(A) simple optimal design method for aerodynamic contractions

Abstract

A new design method is presented for axisymmetric low-speed aerodynamic contractions. The method is based on the finite-difference solution of the boundary value problem for the velocity potential function, which is formulated in the bodyfitted, stretched, nonorthogonal and curvilinear coordinate system. The curvature of the contraction contour was represented by a four-parameter family of polynomial curves, reduced in number by two compared with the six parameters used in the literature. For selected values of contraction ratio, design charts have been presented from which flow uniformity at contraction exit and safety margin, calculated by using Stratford``s formula for boundary layer separation, can be read in terms of contraction parameters. It has been shown that the aerodynamics of contraction is mainly dependent on two parameters out of four, and therefore the design procedure can be simplified very much. Because the method has been formulated in terms of velocity potential function contrary to the existing methods, it can be extended to the design of full three-dimensional contruactions.