“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 Petroski1 1.1 An Overview: The Role of Computational Aerodynamics What is computational aerodynamics (CA)? Theoretical aerodynamics has always providedinsights 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 problems provided important insights which aerodynamicists used as a basis for developing aerodynamic conceptsand understanding experimental results. However, aerodynamic design was carried out experimentally; 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 governingequations 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 availablein the late ’60s, and started providing valuable design information for aerodynamics. Typically, they provided three-dimensional solutions for linear aerodynamics 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 proponentsclaimed that computational aerodynamics would replace 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 computationalaerodynamics 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
1-2 Applied Computational Aerodynamics Computational aerodynamics is one of the most important technologies in the development of advanced vehicles. Many engineersare actively involved in design and analysis using computational aerodynamics. Although numerous books have appeared describing the basic theory of computational fluid dynamics (CFD), guidance on the application of these methods is scarce. However, most engineers working in computational aerodynamics are applying these methods, and not developing new algorithms. There is a difference between CFDalgorithm development and application skills. CFD algorithm developers have their specific interests and organizations. They are trying to solve fundamental algorithm problems and usually do not use their codes to do aerodynamic design and analysis. As a result, they generally have a poor understanding of the needs of and demands on the user*. Users must understand the algorithms and assumptionsemployed in the methods, and an education in the effective use of the computational aerodynamics methods in engineering design and analysis. The ability to approach aerodynamics problems using computational methods, assess the results, and make engineering decisions requires very different skills and attitudes than those associated with fundamental algorithm development. Although you cannot use a...