1. Introduction “Users should approach all software with prudent caution and healthy skepticism, for the history of science and engineering, including the still-young history of software engineering, is littered with failed promises.” Henry Petroski 1 1.1 An Overview: The Role of Computational Aerodynamics What is computational aerodynamics (CA)? Theoretical aerodynamics has always provided insights to aerodynamicists through solutions of the governing equations of fluid mechanics. However, before computers became widely available the application of theoretical aerodynamics to specific problems was frequently impractical. Nevertheless, theoretical results from simplified model prob- lems provided important insights which aerodynamicists used as a basis for developing aerodynamic concepts and understanding experimental results. However, aerodynamic design was carried out ex- perimentally; primarily in wind tunnels. Starting nearly thirty years ago, and becoming increasingly important in the last decade, computational aerodynamics has become an important precursor and supplement to the use of the wind tunnel. Computational aerodynamics applies specific solutions of the governing equations of fluid mechanics to the design and analysis of vehicle systems. Usually this means the numerical solution of governing equations rather than numerical evaluation of analytically derived solutions. As soon as computers became available aerodynamicists started using them. The first computational aerodynamics computer programs that were reasonably general and easy to use became widely available in the late ’60s, and started providing valuable design information for aerodynamics. Typically, they provided three-dimensional solutions for linear aero- dynamics problems, and two-dimensional solutions of the nonlinear boundary layer equations. As with any new technology, this capability arose before engineers understood how to integrate it into the existing design process. Initially proponents claimed that computational aerodynamics would re- place wind tunnels. It was well into the ’70s before the early promise matured into a realization of the difficulties that would have to be overcome for computed solutions to replace wind tunnels. The wind tunnel is still in use, and, NASA has recently announced its intention to build two new wind tunnels. In the ensuing years computational aerodynamics has become an identifiable new technology, making important contributions to flight vehicle design. Now, there is a distinct body of knowledge that provides a foundation for work in the field. Monday, January 20, 1997 1-1