Design optimization of natural laminar flow bodies in compressible flow

An optimization method has been developed to design axisymmetric body shapes such as fuselages, nacelles and external fuel tanks with increased transition Reynolds numbers in subsonic compressible flow. The new design method involves a constraint minimization procedure coupled with analysis of the inviscid and viscous flow regions and linear stability analysis of the compressible boundary- layer. In order to reduce the computer time, Granville''s transition criterion is used to predict boundary-layer transitin and to calculate the gradients of the objective function, and linear stability theory coupled with the e to the nth- method is used to calculate the objective function at the end of each design iteration. Use of the method to design an axisymmetric body with extension natural laminar flow is illustrated through the design of a tiptank of a business jet. For the original tiptank, boundary layer transition is predicted to occur at a transition Reynolds number of 6.04 x E + 06. For the designed body shape, a transition Reynolds number of 7.22 x E + 06 is predicted using compressible linear stability theory coupled with the e to the nth-method.