Methods for Optimization of a Launch Vehicle for Pressure Fluctuation Levels and Drag

Abstract

A computational fluid dynamics (CFD) code has been combined with a Genetic Algorithm (GA) to perform a shape optimization study on a two dimensional axisymmetric model of a generic launch vehicle. The objective of this study is to demonstrate a methodology for reducing pressure fluctuations and the axial force coefficient for a launch vehicle throughout a typical ascent trajectory. Due to the high computational expense and difficulty of generating an adequate mesh autonomously, few CFD driven GA optimizations have been conducted. Some of the complexity of this process was alleviated by using a simple two dimensional axisymmetric geometry to model the vehicle. The optimization process involved the GA selecting a set of geometric parameters that define the shape of the vehicle. A grid generator written in FORTRAN created a mesh based on these parameters and a CFD solver calculated the flow parameters. The CFD solver obtains flow parameters that are used to calculate the pressure fluctuation level and axial force coefficient. A pressure fluctuation level minimization study and axial force minimization study were conducted separately using the same CFD model. The results of each optimization study were compared to a baseline geometry having a very similar shape to the Ares I Crew Launch Vehicle. The results of the pressure fluctuation study yielded approximately a 17.5% reduction in the average RMS pressure fluctuation level throughout the ascent trajectory. The axial force minimization study yielded a reduction in the axial force coefficient of approximately 56%. Nomenclature