Drag reduction and shape optimization of airship bodies

摘要

A tool for the numerical shape optimization of axisymmetric bodies submerged in an incompressible flow at zero incidence has been developed. ^Contrary to the usual approach, the geometry of the body is not optimized in a direct way with this method. ^Instead, a source distribution on the body axis was chosen to model the body contour and the corresponding inviscid flow field, with the source strengths being used as design variables for the optimization process. ^Boundary-layer calculation is performed by means of a proven integral method for attached laminar or turbulent boundary layers. ^To determine the transition location, a semi-empirical method based on linear stability theory was implemented recently. ^A commercially available optimizer, as well as an evolution strategy with covariance matrix adaption of the mutation distribution, is applied as optimization algorithms. ^Shape optimizations of airship hulls were performed with this new tool for different Reynolds number regimes. ^The objective was to minimize the drag for a given volume of the envelope and a prescribed air-speed range. ^The results obtained show a high sensitivity of the optimization result to the transition criterion used. ^(Author)